Illumination apparatus

ABSTRACT

An illumination apparatus comprises a plurality of LEDs aligned to an array of directional optical elements wherein the LEDs are substantially at the input aperture of respective optical elements. An electrode array is formed on the array of optical elements to provide at least a first electrical connection to the array of LED elements. Advantageously such an arrangement provides low cost and high efficiency from the directional LED array.

TECHNICAL FIELD

The technical field relates to an illumination apparatus; an opticalelement for an illumination apparatus and a method to manufacture anillumination apparatus. Such an apparatus may be used for domestic orprofessional lighting, for display illumination and for generalillumination purposes.

BACKGROUND

Light-emitting diodes (LEDs) formed using semiconductor growth onmonolithic wafers can demonstrate significantly higher levels ofefficiency compared to incandescent sources. In this specification LEDrefers to an unpackaged LED die (chip) extracted from a monolithicwafer, i.e. a semiconductor element. This is different from packagedLEDs which have been assembled into a package to facilitate subsequentassembly and may further incorporate optical elements such as ahemisphere which increases its size and light extraction efficiency.

In lighting applications, the light from the emitter is directed using aluminaire optical structure to provide the output directional profile.The angular intensity variation is termed the directional distributionwhich in turn produces a light radiation pattern on surfaces in theilluminated environment. Lambertian emitters flood an illuminatedenvironment with light. Non-Lambertian, directional light sources use arelatively small source size lamp such as a tungsten halogen type in areflector and/or reflective tube luminaire, in order to provide a moredirected source. Such lamps efficiently use the light by directing it toareas of importance. These lamps also produce higher levels of visualsparkle, in which the small source provides specular reflectionartefacts, giving a more attractive illumination environment. Further,such lights have low glare, in which the off-axis intensity issubstantially lower than the on-axis intensity so that the lamp does notappear uncomfortably bright when viewed from most positions.

Directional LED elements can use reflective optics (including totalinternal reflective optics) or more typically catadioptric typereflectors, as described for example in U.S. Pat. No. 6,547,423.Catadioptric elements employ both refraction and reflection, which maybe total internal reflection (TIR) or reflection from metallisedsurfaces. A known catadioptric optic system is capable of producing a 6degree cone half angle (to 50% peak intensity) from a macroscopic LEDcomprising a 1×1 mm light emitting element, with an optical element with20 mm final output diameter. The increase in source size arises fromconservation of brightness (etendue) reasons. Further, such an opticalelement will have a thickness of approximately 10 mm, providing a bulkyillumination apparatus. Increasing the cone angle will reduce the finaldevice area and thickness, but also produces a less directional source.

The LED of this example may be replaced by a 10×10 array of LEDs eachfor example 0.1×0.1 mm size, providing the same emitting area. Thisarrangement has a number of performance advantages, including reducedjunction temperature (reducing illumination apparatus cost), reducedoptical element thickness (reducing illumination apparatus cost),reduced current crowding (increasing device efficiency or reducing costfor a given output luminance) and higher current density capability(increasing device luminance or reducing cost for a given outputluminance). It is therefore desirable to reduce the LED size.

It is desirable to reduce the number of electrical connection steps inconnection of such an array of LEDs, to reduce cost. It is furtherdesirable to reduce the area of electrical connection to such LEDs,preferably at least in proportion to the reduction of area of the LED tomaximise emitting area of the chip. It is further desirable to provideelectrical connections to LEDs on opposite surfaces to reduce currentcrowding.

PCT/GB2009/002340 describes a method to form an illumination apparatuswith an array of small LEDs by preserving the separation of the LEDelements from the monolithic wafer in a sparse array and aligning to anarray of optical elements. GB2463954 shows one electrical connectionmethod to LEDs of an LED array, in which the optical input aperture ispositioned between the electrical connections and output aperture of theoptical elements of the array of optical elements.

EP1 890 343 describes LEDs positioned in reflective cups with anovercoating transparent layer. Such devices are not suitable forproviding directional illumination with narrow cone angles.

In addition, other objects, desirable features and characteristics willbecome apparent from the subsequent summary and detailed description,and the appended claims, taken in conjunction with the accompanyingdrawings and this background.

SUMMARY

According to an aspect of the present disclosure there is provided anillumination apparatus whose primary purpose is illumination as opposedto display, comprising: an optical element array structure; and a lightemitting element structure; the optical element array structure and thelight emitting element structure having been provided as respectiveseparate structures before being assembled together; the optical elementarray structure comprising a plurality of optical elements, wherein theoptical elements are catadioptric, reflective or refractive, and theoptical elements are arranged in an array; the light emitting elementstructure comprising a substrate and a plurality of light emittingelements arranged on the substrate; the optical element array structureand the light emitting element structure being arranged such that theoptical elements of the optical element array structure are aligned withthe light emitting elements of the light emitting element structure; andwherein the optical element array structure further compriseselectrodes, hereinafter referred to as optical element electrodes,arranged thereon for providing electrical connection to the plurality oflight emitting elements. The optical element electrodes may be, at leastin part, positioned on a part of the optical elements that has a shapeprofile or a material composition profile of the optical element that isrelated to the catadioptric, reflective or refractive characteristic ofthe optical element. For at least some of the plurality of lightemitting elements a first electrical connection to the light emittingelement may be provided by a first optical element electrode and asecond electrical connection to the light emitting element may beprovided by a second optical element electrode. For at least some of theplurality of light emitting elements a first electrical connection tothe light emitting element may be provided by the optical elementelectrode and a second electrical connection to the light emittingelement may be provided by a support substrate electrode. At least oneoptical element electrode may be formed on a substantially planarsurface formed between at least two optical elements of the opticalelement array structure. The optical element electrodes may be, at leastin part, positioned on a part of the optical elements that has a shapeprofile substantially arranged to provide a contact between the opticalelement electrodes and substrate electrodes. The part of the opticalelements may comprise a transparent polymer material composition. Theoptical elements may comprise a wavelength conversion material. At leastone of the substrate or optical array may further comprise electroniccomponents arranged in the region between light emitting elements of thelight emitting element array. The plurality of light emitting elementsmay cooperate to provide at least one light emitting element stringcomprising at least two light emitting elements connected in series andthe at least one current source may be multiplexed to multiple stringsof light emitting elements.

According to an aspect of the present disclosure there is provided amethod of manufacturing an illumination apparatus whose primary purposeis illumination as opposed to display, the method comprising: providingan optical element array structure; and providing a light emittingelement structure; wherein the optical element array structure and thelight emitting element structure are provided as respective separatestructures, the optical element array structure comprising a pluralityof optical elements, wherein the optical elements are catadioptric,reflective or refractive, and the optical elements are arranged in anarray; the optical element array structure further comprisingelectrodes, hereinafter referred to as optical element electrodes,arranged thereon for providing electrical connection to the plurality oflight emitting elements; the light emitting element structure comprisinga substrate and a plurality of light emitting elements arranged on thesubstrate; and assembling the optical element array structure with thelight emitting element structure such that the optical elements of theoptical element array structure are aligned with the light emittingelements of the light emitting element structure.

According to an aspect of the present disclosure there is provided anoptical element array structure, comprising: a plurality of opticalelements, wherein the optical elements are catadioptric, reflective orrefractive, and the optical elements are arranged in an array; theoptical element array structure being for being assembled with a lightemitting element structure comprising a substrate and a plurality oflight emitting elements arranged on the substrate such that the opticalelements of the optical element array structure are aligned with thelight emitting elements of the light emitting element structure; andwherein the optical element array structure further comprises electrodesarranged thereon for providing electrical connection to the plurality oflight emitting elements when the optical element array structure and thelight emitting element structure are assembled.

According to an aspect of the present disclosure there is provided anarray of optical elements; the optical elements are catadioptricdirectional optical elements; the array of optical elements beingadapted to be aligned with a plurality of light emitting elementsarranged in an array to provide an illumination apparatus;

wherein: the array of optical elements comprises first electrodes,hereinafter referred to as optical element electrodes, thereon arrangedfor providing a first electrical connection to the plurality of lightemitting elements.

The array of optical elements may be adapted to be aligned with theplurality of light emitting elements to provide a light output cone fromthe illumination apparatus with an output cone angle of less than 30degrees.

According to an aspect of the present disclosure there is provided anarray of catadioptric optical elements; the array of catadioptricoptical elements being adapted to be aligned with a plurality of lightemitting elements arranged in an array with each light emitting elementpositioned substantially at an input surface of a respectivecatadioptric optical element, to provide an illumination apparatus,wherein the catadioptric optical elements each comprise: a first sectioncomprising a polymer material with a first refractive index; and asecond section comprising a polymer material with a second refractiveindex greater than the first refractive index; wherein the refractivepart of the catadioptric optical characteristic of each catadioptricoptical element is provided by a respective interface between its firstsection and its second section, and the respective input surface of eachoptical element comprises the input surface of its first section. Thereflective part of the catadioptric optical characteristic of eachcatadioptric optical element may be provided by a reflective surfacecomprised by its second section. The catadioptric optical elements mayeach comprise: the first section is bounded by an input surface beingadapted to be substantially positioned at the light emitting elements, awall surface and a lens surface; the second section is boundedsubstantially by the wall surface and the lens surface of the firstsection and further bounded by a reflecting surface and an outputsurface; such that the first and second sections are capable ofcooperating to direct light from the light emitting elements to anoutput surface. A recess in the input surface may be adapted foralignment with a respective light emitting element of the plurality oflight emitting elements. A filler polymer material may be providedbetween the reflecting surfaces of adjacent optical elements of thearray of optical elements wherein the filler polymer material has asubstantially planar surface substantially in the plane of the inputsurface of at least one of the array of optical elements to provide asubstantially uniform thickness optical element array structure. Thereflective part of the catadioptric optical characteristic of eachcatadioptric optical element may be provided by total internalreflection in the second section.

According to an aspect of the present disclosure there is provided anillumination apparatus comprising an array of catadioptric opticalelements aligned with a plurality of light emitting elements, whereinthe optical elements comprise: a first section comprising a polymermaterial with a first refractive index; and a second section comprisinga polymer material with a second refractive index greater than the firstrefractive index; the refractive part of the catadioptric opticalcharacteristic of each catadioptric optical element is provided by arespective interface between its first section and its second section;and wherein each light emitting element is positioned substantially atan input surface of the first section of its respective optical element.The reflective part of the catadioptric optical characteristic of eachcatadioptric optical element may be provided by a reflective surfacecomprised by its second section.

According to an aspect of the present disclosure there is provided amethod of manufacturing an illumination apparatus; the methodcomprising: forming a monolithic array of light-emitting elements;selectively removing a plurality of light-emitting elements from themonolithic array by adhering them to a first adhesive substrate in amanner that preserves the relative spatial position of the selectivelyremoved light-emitting elements; transferring the plurality of lightemitting elements from the first adhesive substrate to a second adhesivesubstrate in a manner that preserves the relative spatial position ofthe selectively removed light-emitting elements; transferring theplurality of light emitting elements from the second adhesive substrateto a support substrate in a manner that preserves the relative spatialposition of the selectively removed light-emitting elements; wherein theplurality of light-emitting elements that are selectively removed fromthe monolithic array are selected such that, in at least one direction,for at least one pair of the selectively removed light-emitting elementsin the at least one direction, for each respective pair there is atleast one respective light-emitting element that is not selected thatwas positioned in the monolithic array between the pair of selectivelyremoved light-emitting elements in the at least one direction. Theadhesive force of light emitting elements to the second adhesivesubstrate may be greater than the adhesive force of the light emittingelements to the first adhesive substrate. The adhesive force of thelight emitting elements to the support substrate may be greater than theadhesive force of the light emitting elements to the second adhesivesubstrate. The support substrate may comprise an array of opticalelements and the array of light emitting elements may be aligned withthe respective optical elements. The array of light emitting elementsmay be aligned with an optical substrate comprising an array of opticalelements. The support substrate may comprise a planar substrate whereinthe array of light emitting elements is aligned with an opticalsubstrate comprising an optical element array structure.

According to an aspect of the present disclosure there is provided amethod of manufacturing an illumination apparatus; the methodcomprising: forming a first monolithic array of light emitting elements;determining a first plurality of the light emitting elements which passa functional criterion; determining a second plurality of the lightemitting elements which fail the functional criterion; selectivelyremoving a plurality of the passed light emitting elements whoserelative positions in the first monolithic array correspond to desiredrelative positions in a desired non-monolithic array of light emittingelements, the selectively removing being performed in a manner thatpreserves the relative spatial position of the selectively removedpassed light-emitting elements; wherein the plurality of passedlight-emitting elements that are selectively removed from the monolithicarray are selected such that, in at least one direction, for at leastone pair of the selectively removed passed light-emitting elements inthe at least one direction, for each respective pair there is at leastone respective light-emitting element that is not selected that waspositioned in the monolithic array between the pair of removed passedlight-emitting elements in the at least one direction; and forming anon-monolithic array of light-emitting elements with the selectivelyremoved passed light-emitting elements in a manner that preserves therelative spatial position of the selectively removed passedlight-emitting elements; by virtue of which in the formed non-monolithicarray of light emitting elements desired relative positions of thedesired array that correspond to passed light emitting elements in thefirst monolithic array are occupied by passed light emitting elementsand desired relative positions of the desired array that correspond tofailed light emitting elements in the first monolithic array are leftunoccupied. Further light emitting elements may be added to the formednon-monolithic array of light emitting elements in unoccupied desiredrelative positions of the desired array. The further light emittingelements may be from a second monolithic array of light-emittingelements that is different to the first monolithic array oflight-emitting elements. The further light emitting elements may be fromthe first monolithic array of light-emitting elements. The further lightemitting elements may be light emitting elements which have beendetermined as passing the functional criterion. The method may furthercomprise forming a light intensity reduction region on a surface of themonolithic array support substrate aligned with the second plurality oflight emitting elements.

According to an aspect of the present disclosure there is provided amethod of manufacturing an illumination apparatus; the methodcomprising: forming a non-monolithic array of light-emitting elements ona support substrate; for at least some of the light-emitting elements ina first region of the support substrate, measuring their combinedspectral output; providing a first wavelength conversion layer inalignment with the respective light emitting elements of the firstregion, the spectral characteristic of the first wavelength conversionlayer being selected dependent upon the measured combined spectraloutput from the measured light emitting elements of the first region;for at least some of the light-emitting elements in a second region ofthe support substrate, measuring their combined spectral output; andproviding a second wavelength conversion layer in alignment with therespective light emitting elements of the second region, the spectralcharacteristic of the second wavelength conversion layer being selecteddependent upon the measured combined spectral output from the measuredlight emitting elements of the second region. A first region averagewhite point may be provided by virtue of providing the first wavelengthconversion layer in alignment with the respective light emittingelements of the first region; a second region average white point may beprovided by virtue of providing the second wavelength conversion layerin alignment with the respective light emitting elements of the secondregion, and wherein the first region average white point and the secondregion average white point are thereby more similar than they would beif the two regions had been provided with a same wavelength conversionlayer. A first region average white point may be provided by virtue ofproviding the first wavelength conversion layer in alignment with therespective light emitting elements of the first region, a second regionaverage white point may be provided by virtue of providing the secondwavelength conversion layer in alignment with the respective lightemitting elements of the second region, and wherein the first regionaverage white point and the second region average white point may besubstantially the same. The spectral characteristics of the firstwavelength conversion layer may be different to the spectralcharacteristics of the second wavelength conversion layer.

According to an aspect of the present disclosure there is provided amethod of manufacturing an illumination apparatus; the methodcomprising: forming a monolithic light-emitting layer on a firstsubstrate; transferring the monolithic light-emitting layer to anelectromagnetic wavelength band transmitting substrate; selectivelyremoving a plurality of light-emitting elements from the monolithiclight-emitting layer in a manner that preserves the relative spatialposition of the selectively removed light-emitting elements, performingof the selectively removing comprising selectively illuminating themonolithic array of light-emitting elements through the electromagneticwavelength band transmitting substrate with light in the electromagneticwavelength band; forming a non-monolithic array of light-emittingelements with the selectively removed light-emitting elements in amanner that preserves the relative spatial position of the selectivelyremoved light-emitting elements; and aligning the non-monolithic arrayof light-emitting elements with an array of optical elements. The firstsubstrate may be an electromagnetic wavelength band absorbing substrate.

According to an aspect of the present disclosure there is provided amethod of manufacturing an illumination apparatus; the methodcomprising: forming a monolithic array of light-emitting elements madeof a plurality of layers on a substrate, the light emitting elementsbeing inter-connected in the layers they are formed in; selectivelyilluminating a plurality of the light emitting elements with anillumination that separates, at least to an extent, the selected lightemitting elements from the substrate; the illumination further breakingthe connection in the layers between each selectively illuminated lightemitting element and the other light emitting elements; removing theilluminated light-emitting elements from the monolithic array in amanner that preserves the relative spatial position of the removedlight-emitting elements; wherein the plurality of light-emittingelements that are selectively illuminated and removed from themonolithic array are selected such that, in at least one direction, forat least one pair of the selectively illuminated and removedlight-emitting elements in the at least one direction, for eachrespective pair there is at least one respective light-emitting elementthat is not selected that was positioned in the monolithic array betweenthe pair of selectively illuminated and removed light-emitting elementsin the at least one direction. The method may further comprise providinga patterned support layer formed on the plurality of light emittingelements.

By way of comparison with a known illumination apparatus, the presentembodiments advantageously provide a reduced cost electrical connectionapparatus for an illumination apparatus. Advantageously the electricalconnection apparatus is integrated with the optical element andsubstantially at the input aperture of the optical element such thatlight from the LED is collected efficiently. The electrical connectionmay provide a vertical connection path to the LED, reducing currentcrowding and increasing LED efficiency. The area of the electricalconnection may be reduced improving light extraction efficiency. TheLEDs of the array may be connected in parallel, reducing assembly timeand cost and increasing device reliability. Further the opticalthroughput efficiency of an array of catadioptric optical elements isimproved in comparison with known arrays of elements.

A person skilled in the art can gather other characteristics andadvantages of the disclosure from the following description of exemplaryembodiments that refers to the attached drawings, wherein the describedexemplary embodiments should not be interpreted in a restrictive sense.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present disclosure will now be described, by way ofexample only, with reference to the accompanying drawings in which:

FIG. 1 shows a flip chip LED with lateral electrical connections;

FIG. 2 shows a vertical thin film LED;

FIG. 3a shows the respective separate structures of an optical elementarray structure and light emitting element structure before beingassembled together;

FIG. 3b shows an illumination apparatus comprising the respectivestructures of FIG. 3a after being assembled together;

FIG. 4a shows in cross section one catadioptric optical element;

FIG. 4b shows in plan view one catadioptric optical element;

FIG. 5a shows in cross section electrical connection of a light emittingelement to a catadioptric optical element;

FIG. 5b shows in plan view electrical connection of a light emittingelement to a catadioptric optical element;

FIG. 6 shows in cross section a detail of another electrode attachmentapparatus;

FIG. 7 shows in cross section a detail of another electrode attachmentapparatus;

FIG. 8 shows in cross section a detail of another electrode attachmentapparatus;

FIG. 9 shows a further illumination apparatus comprising an electricalconnection apparatus integrated with an optical apparatus;

FIG. 10 shows a detail of an electrical connection apparatus integratedwith an optical apparatus;

FIG. 11 shows one array of optical elements with integrated electrodes;

FIG. 12 shows a further array of optical elements with integratedelectrodes;

FIG. 13 shows a further array of optical elements with integratedelectrodes;

FIG. 14 shows a further array of optical elements with integratedelectrodes;

FIG. 15a shows a method for self assembly of an LED array;

FIG. 15b shows a self assembled array of LEDs;

FIG. 15c shows a method to connect an array of optical elements withintegrated electrical connections to the array of FIG. 15 b;

FIG. 16 shows in plan view one electrical connector array integratedwith an array of optical elements;

FIG. 17 shows in plan view a further electrical connector arrayintegrated with an array of optical elements;

FIG. 18 shows in plan view a further electrical connector arrayintegrated with an array of optical elements;

FIG. 19 shows a detail of the LED elements of FIG. 20 in which aredundant LED is provided;

FIG. 20a shows in plan view an array of optical elements prior toforming an electrode array;

FIG. 20b shows in plan view a mask comprising an aperture array;

FIG. 20c shows in plan view an optical array with an electrode arrayformed with the mask of FIG. 20 b;

FIG. 20d shows in cross section the optical array of FIG. 20 c;

FIG. 20e shows in plan view an optical element;

FIG. 20f shows in plan view an optical element in which a first regionis electrically isolated from a second region;

FIG. 20g shows in cross section an array of optical elements of FIG. 20f;

FIG. 20h shows in plan view an optical element;

FIG. 20i shows in plan view an optical element in which a first regionis electrically isolated from a second region;

FIG. 21a shows a method to form an array of electrode elements on anoptical element;

FIG. 21b shows a further method to form an array of electrode elementson an optical element;

FIG. 21c shows a method to form a photoresist layer on an opticalelement;

FIG. 21d shows the optical element of FIG. 21c following an etch step;

FIG. 22 shows a connection apparatus for an array of LEDs;

FIG. 23 shows a further connection apparatus for an array of LEDs;

FIG. 24 shows a further connection apparatus for an array of LEDs;

FIG. 25 shows a further connection apparatus for an array of LEDs;

FIG. 26 shows a further connection apparatus for an array of LEDs;

FIG. 27 shows a further connection apparatus for an array of LEDs;

FIG. 28 shows a further connection apparatus for an array of LEDs;

FIG. 29 shows a further connection apparatus for an array of LEDs;

FIG. 30 shows a further connection apparatus for an array of LEDs;

FIG. 31 shows a further connection apparatus for an array of LEDs;

FIG. 32 shows a further connection apparatus for an array of LEDs;

FIG. 33 shows a further connection apparatus for an array of LEDs;

FIGS. 34a-34d show a method to form an array of electrode connections;

FIGS. 35a-35c show a further method to form an array of electrodeconnections;

FIGS. 35d-f show a further method to form an array of electrodeconnections;

FIGS. 35g-i show a further method to form an array of electrodeconnections;

FIGS. 36a-36g show a method to form an array of light emitting elements;

FIG. 36h shows a mothersheet support substrate comprising multiplearrays of light emitting elements;

FIGS. 36i-36j show a further method to form an array of light emittingelements;

FIGS. 37a-37d show a further method to form an array of light emittingelements;

FIGS. 38a-38g show a further method to form an array of light emittingelements with increased yield;

FIG. 39a shows schematically a string of LEDs comprising correction oflight emitting element fault;

FIG. 39b shows schematically a further string of LEDs comprisingcorrection of light emitting element fault;

FIG. 40 shows in plan view an array of light emitting elements;

FIG. 41 shows a wafer comprising an array of light emitting elements;

FIG. 42a shows a composite substrate comprising multiple arrays of lightemitting elements;

FIGS. 42b and 42c show regions of the composite substrate;

FIG. 43 shows a phosphor array for use with the composite substrate ofFIG. 42 a;

FIG. 44 shows a method to form a phosphor array;

FIG. 45 shows a staggered electrode string; and

FIG. 46a-f shows a method to extract an array of light emitting elementsformed on a light absorbing epitaxial substrate.

DETAILED DESCRIPTION

The following detailed description is merely exemplary in nature and isnot intended to limit the present disclosure or the application and usesof the present disclosure. Furthermore, there is no intention to bebound by any theory presented in the preceding background or thefollowing detailed description.

A known type of flip chip LED 16 comprising one example of a lightemitting element 42 with lateral configuration is shown with electricalconnections in FIG. 1. A substrate 2 such as sapphire has epitaxiallayers formed on its surface 3. Typically a gallium nitride devicecomprises an n-doped layer 4, a multiple quantum well structure 6 and ap-doped layer 8 with a p-electrode 10. In the region 12, a portion ofthe p-layer and structure 6 is removed to provide a contact electrode 14to be formed in contact with the n-doped layer 4. This arrangementsuffers from current crowding in the region 13, reducing the maximumlight output that can be obtained from the device. Solder connections18, 20 are formed on electrodes 22, 24 respectively, mounted on asupport substrate 26.

In this specification, the term solder connections refers to knownelectrical connections including those formed by heating or by pressureor combination of heating and pressure applied to suitable electricallyconductive materials.

FIG. 2 shows a vertical thin film (VTF) configuration LED 17 comprisinganother example of a light emitting element 42 in which the n-dopedlayer 4 has been separated from the substrate 2, for example by means oflaser lift off. An electrode 28 is applied to the p-doped layer 8 andattached by means of a solder element 30 to an electrode 32 formed onthe substrate 26. The n-doped layer may optionally have a transparentelectrode 34 formed on its surface, and a further electrode 36 toprovide a solder 38 contact to an input electrode 40. Such a VTFconfiguration advantageously has reduced current crowding compared tothe arrangement of FIG. 1.

However, the VTF configuration needs an electrode connection on the topsurface, and so often requires a wire bonding process. In the case oflarge arrays of small light emitting elements, this would require alarge number of time consuming wire bonds to be formed. Further, wirebonding technology may have limited positional accuracy so that a largenon-emitting bond pad area on electrode 36 is required to providereliable wire bonding. For example, the wire bond pad size may be 100micrometers in size, which may be comparable to the desirable size ofthe LED light emitting element 42. However, microscopic LEDs similar tothose manufactured using the method of PCT/GB2009/002340 achieve smallbond pad size due to the use of photolithographically defined electrodeson large accurate arrays of small light emitting elements.

FIG. 3a shows an embodiment wherein a directional illumination apparatusprior to assembly comprises a light emitting element structure 43comprising a substrate 67 and an array of light emitting elements 42comprising VTF LEDs 17 arranged on the substrate 67; and an opticalelement array structure 41 comprising a plurality of optical elements 1.

After assembly by aligning the structures 41, 43, and translating indirection 65 such that the optical elements 1 of the optical elementarray structure 41 are aligned with the light emitting element 42 of thelight emitting element structure 43, an illumination apparatus as shownin FIG. 3b is formed. The optical element structure 41 further comprisesoptical element electrodes 56 arranged thereon for providing electricalconnection to the plurality of light emitting elements 42. Further,electrical connection joints 79 are provided to facilitate connectionbetween the two respective substrates. Joints 79 may be provided bysolder (that may be eutectic solder), conductive adhesive or other knownelectrical connection material systems and may be arranged on one orboth of the structures 41,43. The light emitting elements 42 are furtherelectrically connected by means of optical element electrode 56 andsubstrate electrode 64. Optical element electrode 56 thus provides afirst electrical connection to the light emitting element 42. Aconnecting structure 54 is formed in or attached to the optical element1 on which the optical element electrode 56 is formed. This provides acontact between the optical element electrode 56 and the substrateelectrode 62 or substrate electrode 58. The substrate electrode 64provides a second electrical connection to the light emitting element42. Thus for at least some of the plurality of light emitting elements42 a first electrical connection to the light emitting element isprovided by the optical element electrode 56 and a second electricalconnection to the light emitting element is provided by a supportsubstrate electrode 58, 62 or 64

The light emitting elements 42 can be operated as one or more strings oflight emitting elements 42 by connecting the n-doped layer of one lightemitting element 42 to the p-doped layer of an adjacent light emittingelement 42. The optical element array structure 41 and light emittingelement structure 43 thus cooperate to provide at least one lightemitting element string comprising at least two light emitting elements42 connected in series. Active or passive electronic control elements66, for example transistors, rectifying diodes or resistors may bepositioned between substrate electrodes 62 and 64, providing someelectrical control of light emitting elements 42 within the array andbetween adjacent optical elements. The elements 66 may form anelectrical circuit with light emitting elements 42 including being inseries or parallel with at least some of them. The optical elementelectrodes 56 are, at least in part, positioned on a part (connectingstructure 54) of the optical elements 1 that has a shape profilesubstantially arranged to provide a contact between the optical elementelectrodes 56 and substrate electrodes 58, 62. The part (connectingstructure 54) may comprise a transparent polymer material composition.

The light emitting elements 42 and substrate electrodes 58, 62, 64 maybe formed at least in part on a substrate 67 that may comprise anelectrically insulating layer 50 and a heat conducting layer 52 whichprovide a heat sink function and may for example be a metal core printedcircuit board. Alternatively, the layer 50 may have sufficient rigiditythat it can comprise the substrate 67 without additional layer 52 duringprocessing of the light emitting elements 42. Substrate 67 may betypically planar and may be in the form of a mothersheet supportsubstrate with large area to achieve the processing of many lightemitting elements in parallel, reducing cost. The substrate 67 or theoptical element array structure 41 may comprise electronic components 66arranged in the region between light emitting elements 42 of the lightemitting element array. The electronic components may provide additionalfunctions to the array of light emitting elements 42 and may be nonlight-emitting.

Thus the embodiment comprises an array of optical elements 1 in whichthe optical elements 1 are catadioptric. Alternatively, the opticalelements 1 may be reflective or refractive. The array of opticalelements 1 are adapted to be aligned with a plurality of light emittingelements 42 (for example LEDs 16 or LEDs 17) arranged in an array toprovide an illumination apparatus wherein the array of optical elements1 comprises electrodes thereon arranged for providing electricalconnection to the plurality of light emitting elements 42.

Thus an illumination apparatus whose primary purpose is illumination asopposed to display, may comprise an optical element array structure 41;and a light emitting element structure 43; the optical element arraystructure 41 and the light emitting element structure 43 having beenprovided as respective separate structures before being assembledtogether; the optical element array structure 41 comprising a pluralityof optical elements 1, wherein the optical elements 1 are catadioptric,reflective or refractive, and the optical elements 1 are arranged in anarray; the light emitting element structure 43 comprising a substrate 67and a plurality of light emitting elements 42 arranged on the substrate;the optical element array structure 41 and the light emitting elementstructure 43 being arranged such that the optical elements 1 of theoptical element array structure 41 are aligned with the light emittingelements 42 of the light emitting element structure 43; and wherein theoptical element array structure 41 further comprises electrodes 56,hereinafter referred to as optical element electrodes 56, arrangedthereon for providing electrical connection to the plurality of lightemitting elements 42.

Thus a method of manufacturing an illumination apparatus whose primarypurpose is illumination as opposed to display, may comprise: providingan optical element array structure 41; and providing a light emittingelement structure 43; wherein the optical element array structure 41 andthe light emitting element structure 43 are provided as respectiveseparate structures; the optical element array structure comprising aplurality of optical elements 1, wherein the optical elements arecatadioptric, reflective or refractive, and the optical elements 1 arearranged in an array; the optical element array structure 41 furthercomprising electrodes 56, hereinafter referred to as optical elementelectrodes 56, arranged thereon for providing electrical connection tothe plurality of light emitting elements 42; the light emitting elementstructure comprising a substrate 67 and a plurality of light emittingelements 42 arranged on the substrate; and assembling the opticalelement array structure 41 with the light emitting element structure 43such that the optical elements 1 of the optical element array structure41 are aligned with the light emitting elements 42 of the light emittingelement structure 43.

Thus an optical element array structure 41, comprises: a plurality ofoptical elements 1, wherein the optical elements 1 are catadioptric,reflective or refractive, and the optical elements 1 are arranged in anarray; the optical element array structure 41 being for being assembledwith a light emitting element structure 43 comprising a substrate 67 anda plurality of light emitting elements 42 arranged on the substrate 67such that the optical elements 1 of the optical element array structure41 are aligned with the light emitting elements 42 of the light emittingelement structure 43; and wherein the optical element array structure 41further comprises electrodes 56 arranged thereon for providingelectrical connection to the plurality of light emitting elements 42when the optical element array structure 41 and the light emittingelement structure 43 are assembled.

The optical elements 1 are directional optical elements arranged toconvert the substantially Lambertian output of the light emittingelements 42 into a narrower cone 55 of light beams with a smaller solidangle than the Lambertian output. The cone angle of output is defined asthe half angle for half of the peak intensity and may be about 6 degreesfor a narrow collimation angle and may be about 45 degrees for a wide(but still with some directionality) cone angle and is typically about30 degrees or less for directional illumination systems. By way ofcomparison, Lambertian output cone angle is 60 degrees. To achievereduced cone angle of light beams 55, directional optics that have asignificant etendue varying property, requiring an output aperture size11 that is significantly larger than light emitting element 42 size arerequired. For example, a catadioptric optical element arranged for usewith a 100 micrometres width light emitting element 42 may have a size11 of approximately 2 mm. Narrow cone angles in particular requirenon-imaging catadioptric optics. By way of comparison reflective cupssuch as described in EP1 890 343 are unsuitable for providing narrowcone angles due to relatively shallow depth required in order to placethe LED and electrodes in the cup. This citation shows LEDs which mustbe placed on top of the cups and then connected in a serial (wirebonded)process to the reflective cups. The light emitting element structuretherefore is not provided as a separate structure, (but as individualLEDs), before assembly to the optical element array structure

An array of optical elements 1 may be provided wherein the opticalelements 1 are catadioptric directional optical elements; the array ofoptical elements 1 being adapted to be aligned with a plurality of lightemitting elements 42 arranged in an array to provide an illuminationapparatus; wherein: the array of optical elements 1 comprises firstelectrodes 56, hereinafter referred to as optical element electrodes 56,thereon arranged for providing a first electrical connection to theplurality of light emitting elements 42. The array of optical elements 1may be adapted to be aligned with the plurality of light emittingelements 42 to provide a light output cone angle of light beams 55 fromthe illumination apparatus with an output cone angle of less than about45 degrees and preferably less than about 30 degrees.

Light emitting element 42 arrays and efficient collimating opticalelements 1 of the optical element array structure 41 can be fabricatedwith highly precise separation, for example as described inPCT/GB2009/002340. Advantageously the present embodiments provideelectrical connection to electrode 36 for each light emitting element ofthe array in a single step to reduce assembly cost. Further the lightemitting elements are arranged as VTF configuration light emittingelements with lower current crowding effects. The position of theelectrode elements can be precisely defined (for example byphotolithography) so that their size can be reduced compared to thatnecessary for wire bonding, and so the loss of light due to shielding bythe electrode can advantageously be reduced. Further, the light emittingelement are sparsely separated, so that the gaps between the lightemitting elements 42 on the optical elements 1 and the support substratecan be used for electrodes in addition to further electronic componentsincluding for example resistors, diodes, control signal receivers forInfra Red or RF or integrated circuits to increase device functionality.The light emitting elements may be conveniently attached to a heat sinkelement to reduce junction temperature and increase device efficiency,further enabling higher current densities to be used, thus providinghigher efficiency.

The optical elements 1 may have a spacing region 72 to relieve bendingstress in structure 41, and thus provide a flat structure for uniformattachment to the light emitting element array. The array has a topsurface 71 which may be planar, may be conveniently anti-reflectioncoated or may have a surface structure to provide some further opticalfunction to the output ray bundle 55 such as diffuser, lenticular lensarray, lens array or prism array.

Thus the embodiment comprises an array of optical elements 1 wherein theoptical elements 1 are catadioptric. The optical elements 1 may also bereflective or refractive as will be described below. The array ofoptical elements 1 are adapted to be aligned with a plurality of lightemitting element 42 arranged in an array to provide an illuminationapparatus wherein the array of optical elements 1 comprises firstoptical element electrodes 56 thereon arranged for providing a firstelectrical connection to the plurality of LED light emitting elements42. Further, an illumination apparatus comprises the array of opticalelements 1 aligned with a plurality of light emitting elements 42.

A single catadioptric optical element 1 of array is shown in crosssection in FIG. 4a and plan view in FIG. 4b . The optical element 1 isformed on the substrate 46 and comprises a first section 35 comprising acavity and a polymer material with a first refractive index and a secondsection 49 comprising a polymer with a second refractive index greaterthan the first refractive index. The cavity 35 is bounded substantiallyby wall surface 85, lens surface 87 and input surface 81 of size definedby the aperture 37 of the optical element 1. The second section isbounded by the surfaces 85, 87 and additionally by reflecting surface 45and output surface 83, of size defined by the aperture 39 of the opticalelement 1. Both sections comprise polymer materials, wherein therefractive index of the cavity 35 material 47 is lower than therefractive index of the second section material 49. For example, thematerial 47 may be a silicone material with refractive indexapproximately 1.4 and the material 49 may be a cross linked UV curedpolymer with refractive index 1.56. The first cavity 35 section andsecond reflective sections are capable of cooperating to direct lightfrom the light emitting elements to the output surface 83 andsubsequently through the substrate 46 (which may be formed in thematerial 49 or may for example be a glass substrate). In particular,substantially all light emitted in a forward or lateral direction isdirected through the output aperture 39 into a narrower cone angle thanfrom the original (typically Lambertian) cone.

Thus an array of catadioptric optical elements 1 may be provided; thearray of catadioptric optical elements being adapted to be aligned witha plurality of light emitting elements 42 arranged in an array with eachlight emitting element 42 positioned substantially at an input surface81 of a respective catadioptric optical element 1, to provide anillumination apparatus, wherein the catadioptric optical elements 1 eachcomprise: a first section 35 comprising a polymer material with a firstrefractive index; and a second section 49 comprising a polymer materialwith a second refractive index greater than the first refractive index;wherein the refractive part of the catadioptric optical characteristicof each catadioptric optical element is provided by a respectiveinterface between its first section 35 and its second section 49, andthe respective input surface of each optical element comprises the inputsurface of its first section 81. The reflective part of the catadioptricoptical characteristic of each catadioptric optical element is providedby a reflective surface 45 comprised by its second section 49. The firstsection 35 may be bounded by an input surface 81 being adapted to besubstantially positioned at the light emitting elements 42, a wallsurface 85 and a lens surface 87; the second section 49 is boundedsubstantially by the wall surface 85 and the lens surface 87 of thefirst section and further bounded by a reflecting surface 45 and anoutput surface 83; such that the first and second sections 35, 49 arecapable of cooperating to direct light from the light emitting elements42 to an output surface 83. A recess 74 in the input surface 81 may beadapted for alignment with a respective light emitting element of theplurality of light emitting elements 42. A filler polymer material 101may be comprised between the reflecting surfaces 45 of adjacent opticalelements of the array of optical elements 1 wherein the filler polymermaterial 101 has a substantially planar surface 97 substantially in theplane of the input surface 81 of at least one of the array of opticalelements 1 to provide a substantially uniform thickness optical elementarray structure 41. The reflective part of the catadioptric opticalcharacteristic of each catadioptric optical element 1 may be provided bytotal internal reflection in the second section 49.

An illumination apparatus may thus comprise an array of catadioptricoptical elements 1 aligned with a plurality of light emitting elements42, wherein the optical elements 1 comprise: a first section 35comprising a polymer material with a first refractive index; and asecond section 49 comprising a polymer material with a second refractiveindex greater than the first refractive index; the refractive part ofthe catadioptric optical characteristic of each catadioptric opticalelement is provided by a respective interface between its first section35 and its second section 49; and wherein each light emitting element 42is positioned substantially at an input surface 81 of the first section35 of its respective optical element 1. The reflective part of thecatadioptric optical characteristic of each catadioptric optical element1 may be provided by a reflective surface 45 comprised by its secondsection 49.

Advantageously, such an arrangement provides for highly efficientcoupling of light. In particular, the cavity does not comprise air andso Fresnel reflections are reduced, thus increasing output efficiencyand reducing illumination apparatus cost. Further, by way of comparisonwith known macroscopic LED systems of thickness typically 10 mm, the lowthickness of the present embodiments reduce the internal absorption inthe materials 47, 49. Advantageously, the low thickness reduces theamount of materials so that higher cost per unit volume materials can beused without increasing overall device cost.

The input surface 81 is adapted to be substantially positioned at thelight emitting elements 42. The surface 81 may be plane, or for examplemay comprise a recess 74 may be formed to provide a region for the lightemitting element 42 to be inserted so that in operation light directedlaterally from the light emitting element 42 is collected by the wallsurface 45 of the optical element 1. Typical thin film LED lightemitting elements have a thickness of less than 10 micrometres. Thus fora 100 micrometre width LED device, thickness 29 may be about 1 mm,thickness 57 may be about 0.5 mm and thickness 53 may be about 50micrometres or less. Alternatively, the recess walls may have a heightto accommodate a light emitting element mounted on a support substrate,such as sapphire wafer or silicon, in which case its thickness may begreater.

As shown in FIG. 4b , the output aperture 39 may be hexagonal in shape,or alternatively may be other shapes such as round or square forexample. The optical element electrode 56 may comprise a thin stripcomprising a linear feature to advantageously optimise the proportion ofthe reflector that uses total internal reflection, TIR rather thanmetallic reflection, thus increasing efficiency. The electrode 36 may beextended in an orthogonal direction to the optical element electrode 56to reduce alignment tolerance between the two components.

A schematic detail of a single light emitting element 42 and alignedoptical element 1 of FIG. 3 is shown in cross section in FIG. 5a andplan view in FIG. 5b . For illustrative convenience, the height of therecess 74 in the input surface 81 has been increased. Electrode 56 isformed on part of the surface 81 and is thus in the region that providesan optical imaging function of the catadioptric optical element 1. Thep-doped layer 8 of LED light emitting element 42 is attached to opticalelement electrode 56 by means of solder 38. Thus the optical elementelectrodes 56 are, at least in part, positioned on a part (such assurface 81) of the optical elements 1 that has a shape profile or amaterial composition profile of the optical element 1 that is related tothe catadioptric, reflective or refractive characteristic of the opticalelement. The electrode 56 is positioned on part of the surface 81 of theoptical elements 1 so that it is near an input aperture defined byaperture 37 in plane 61 (shown in FIG. 4a ) of the optical elements 1.That is the surface 81 is near the input aperture within less than about10% of the thickness 29 of the optical element 1, and preferably lessthan about 5% of the thickness 29 of the optical element 1. Further theoptical element electrodes 56 are positioned on part of the opticalelements 1 that is between the input aperture and an output aperture ofthe optical elements 1. Advantageously, as the optical element electrode56 is on the surface 81, the light emitting element 42 is thus arrangedto be at a location from which light can be efficiently collected by thecatadioptric optical element 1.

The n-doped layer 4 of LED light emitting element 42 is connected bymeans of reflective electrode 34 and solder 30 to substrate electrode48. The optical element electrode 56 is connected to substrate electrode58 by means of solder 60. Thus the first optical element electrodes 56are further arranged for providing an electrical connection to substrateelectrode 58. The first optical element electrodes 56 are thus at leastin part, positioned on a part of the optical elements 1 (such asconnecting structure 54) that has a shape profile substantially arrangedto provide a contact between the first optical element electrodes 56 andthe substrate electrodes 58. Thus the optical elements 1 furthercomprise pillar regions such as structures 54 wherein the first opticalelement electrodes 56 are, at least in part, positioned on the pillarregions.

The solder attachment method may be provided (using the example ofsolder 38) by forming metal layers such as palladium or other knownelectrode material layers (not shown) on the optical element electrode56 and the electrode 36. A further metal layer such as an indium layermay be formed on one of the palladium layers. On heating for example toabout 180 degrees Celsius and application of pressure between the twoelectrodes 36, 56 the palladium and indium alloy, providing amechanical, thermal and electrical joint. Such alloying step canadvantageously be provided in parallel across the array of lightemitting elements 42 and optical elements 1 with electrodes 56, reducingassembly cost. The metal layers may comprise other known electrodematerials including but not limited to gold, indium tin oxide, titanium,aluminium, tin, platinum and nickel.

For a white light source, the light emitting elements of the array maycomprise separate red, green and blue LEDs. However, a wavelengthconversion layer 76 for example comprising a phosphor material may beincorporated as shown in FIG. 6 in combination with a blue emission LED42. The phosphor layer 76 may be formed on the surface 81 and theoptical element electrode 56 positioned on the internal surface 75 ofthe layer 76. Such a layer 76 remains related to the catadioptric,reflective or refractive characteristic of the optical element. Theoptical elements 1 thus comprise a wavelength conversion material. Afurther index matching material 51 may be inserted to improve opticalcoupling between the light emitting element and the array of opticalelements 1. FIG. 6 further shows an alternative cross section to thatshown in FIG. 4 wherein the connecting structure 54 comprises part ofthe surface 81, and optical element electrode 56 attaches to thesubstrate electrode 58 by means of solder 60. Such an embodimentadvantageously reduces the complexity of the optical element. A furtherelectrically and thermally conductive pillar 80 may be incorporated tomount the light emitting element further within the cavity 35 of theoptical element.

FIG. 7 shows an alternative cross section to that shown in FIG. 6wherein a wavelength conversion layer region 84 is formed afterelectrode connection of the light emitting element 42. A furtherconductive pillar 88 may be added to the top of the light emittingelement 42 or to the surface 81 to provide a connection element toincrease the thickness of the region 84 above the light emitting element42 to the optical element electrode 56. Such embodiment provides theelectrode to be formed and light emitting element 42 to be attachedprior to the introduction of the phosphor layer. The material 84 couldfurther incorporate a conductive material so as to provide electricalconnection between the electrode 90 of the light emitting element 42 andelectrode 56. In this case, further dielectric layers (not shown) may beapplied to the light emitting element to prevent undesirable shortcircuits.

FIG. 8 shows an embodiment wherein the optical element comprises areflective optical element 94 in which the walls of the reflectiveelement are a formed metal reflector. An electrode support element 96with electrode 98 and surface 81 may be formed near the input aperturewith optical element electrode 98 attached to the reflector 94 toprovide a conductive path to substrate electrode 58. The electrodesupport element 96 may further comprise a hemispherical output shape tooptimise light output coupling efficiency. Advantageously such anoptical element 94 may have a lower cost than the catadioptric opticalelements described previously, although it may have lower efficiency.This arrangement may be suited to wider angle optical output, forexample greater than about 30 degrees HWHM (half width half maximum),collimation compared to less than about 10 degrees HWHM possible withcatadioptric optical elements.

FIG. 9 shows a further embodiment, shown in detail in FIG. 10 in whichan array of lateral configuration LEDs 16 comprising light emittingelements 42 is used with first optical element electrodes 56 and secondoptical element electrodes 100, to provide first and second connectionto the light emitting elements 42. In an LED string, the second opticalelement electrode 100 for one light emitting element 42 becomes thefirst second optical element electrode 56 for adjacent light emittingelements 42. Both electrodes are positioned on a structure 41 comprisingan array of catadioptric optical elements 1, and provide electricalconnection on part of the surface 81 in the light directing part of thecatadioptric optical element 1. Thus for at least some of the pluralityof light emitting elements 42 a first electrical connection to the lightemitting element 42 is provided by a first optical element electrode 56and a second electrical connection to the light emitting element isprovided by a second optical element electrode 100.

The surface 45 may be coated with a reflective material 102, and the gapbetween the optical elements 1 filled with a material 101, which may bethe same as material 49 to provide a uniform structure and optimiseflatness for attachment of electrodes 56, 100 and LEDs 16. Thus thecatadioptric optical elements may further comprise a filler polymermaterial 101 between the reflecting surfaces of adjacent opticalelements 1 of the array of optical elements 1. The filler polymermaterial 101 may have a substantially planar surface 97 substantially inthe plane of the surface 81 of at least one of the array of opticalelements 1 to provide a substantially uniform thickness array of opticalelements. Advantageously, such an embodiment may advantageously providea flexible optical and electronic structure.

Thus the array of optical elements 1 comprises second optical elementelectrodes 100 thereon arranged for providing a second electricalconnection to the plurality of light emitting elements 16. Thus firstand second electrical connections to each of the plurality of lightemitting elements are provided by the respective first and secondoptical element electrodes. Further at least one first optical elementelectrode 100 is formed on a substantially planar surface 97 formedbetween at least two optical elements 1 of the array of optical elements1.

Further heat spreader elements 103 may be incorporated between the lightemitting element 42 and support substrate 67 to advantageously reducethe thermal resistance of the mounted light emitting element 42. Theheat spreader may comprise for example a metal layer or a silicon layer.Further electronic components 66 may be arranged in the regions betweenthe optical elements 1 of the array. Such arrangement provides a firstsubstrate that provides electronic and optical functions and a secondsubstrate that provides heatsinking functions. Advantageously theembodiment does not require bonding of electrodes onto the heat spreader103, simplifying the optical structure of the substrate 67, thusreducing cost. In other embodiments, such heat spreaders 103 can also beused in combination with VTF configuration LEDs 17.

FIG. 11 shows an optical element array structure 41 comprising an arrayof optical elements 1 comprising catadioptric optical elements for usein the illumination apparatus similar to that shown in FIG. 3. Thesurfaces 45 are coated with a reflective material 102 and an additionalmaterial 101 is incorporated between the optical elements 1.

FIG. 12 shows a reflective compound parabolic concentrators 104 (CPC)for use in illumination apparatus. Each element may incorporate a recessfor electrode attachment and insertion of the light emitting element 42.Advantageously such an arrangement may provide lower degree ofcollimation than the element of FIG. 11 with a more uniform spot profileand more defined penumbra in the output illumination beam structure.

FIG. 13 show reflective CPCs formed from structures 108 with areflective coating 102 incorporating further hemispherical optics 110into which light emitting elements 42 are inserted. Hemispherical opticsadvantageously couple light from the light emitting element into airefficiently and can be incorporated into the same moulding as thestructures 108 or added in a secondary process. Such a structureadvantageously uses less material than that shown in FIG. 12. Thus thepart of the surface 81 of optical element 1 on which the electrodes 56are formed comprises part of a surface of a refractive lens 110.

FIG. 14 shows an alternative embodiment of optical element arraystructure 41 in which the cavity 35 is filled with air and hemisphericaloptics 110 are incorporated in the structure and have the electrodestructure applied. Advantageously such a structure has a lower thicknessand higher spatial density of optical elements 1 than the opticalstructure in FIG. 3.

To achieve high precision of separation, the plurality of light emittingelements 42 such as LEDs 16 or LEDs 17 of the present embodiments may befrom a monolithic wafer with their separations preserved, and whereinthe plurality of passed light-emitting elements that are selectivelyremoved from the monolithic array may be selected such that, in at leastone direction, for at least one pair of the selectively removed passedlight-emitting elements in the at least one direction, for eachrespective pair there is at least one respective light-emitting elementthat is not selected that was positioned in the monolithic array betweenthe pair of removed passed light-emitting elements in the at least onedirection, as described in PCT/GB2009/002340.

Alternatively, the separation of the light emitting elements may beachieved by means of self assembly. FIG. 15a shows the self assembly oflight emitting element into a precision array. A container 118 is filledwith a liquid 120 and diced LED 122. A substrate 124 has an array ofconductive adhesive regions 126 (which may be solder regions),interspersed by non adhesive regions 128 (such as resist) formed on itssurface. As shown in FIG. 15b , the LEDs 122 may be coated so as topreferentially attach in a first orientation 132 with either p-dopedlayer up or a second orientation 130 with n-doped layer up. FIG. 15cshows the alignment of the LEDs 122 with an optical element arraystructure 41. In operation, the LEDs 122 of the array are typicallyconfigured with n-doped layer of a first element attached to the p-dopedlayer of an adjacent LED 122. In such a self-assembled device, theorientation of the LED 122 may not be clear until the elements aretested. In this case, the electrodes may require reconfiguring to setthe appropriate polarities. The orientation of the LED 122 may bedetermined by inspection or electrical testing. For example electrodes134 may be cut in regions 136, for example by means of laser cutting.Advantageously connectivity to self assembled LED 122 arrays isprovided. By way of comparison, if the LEDs 122 were lateralconfiguration type, each LED 122 would need to have a rotationalorientation so that for example the etched regions 12 in FIG. 1 arealigned up with the relevant region in each adhesive region 126.Advantageously in the present embodiments, the rotational orientation isnot critical as the devices are VTF configuration type and connected tothe electrode on the optic array.

FIG. 16 shows in plan view light emitting element 42, connectingstructure 54 and optical element electrode 56 for optical elements 1 ofthe present embodiments. Advantageously, the light emitting elements ofthe array may be arranged in strings to provide a number of lightemitting elements to be connected in series. In this embodiment, thehexagonal output aperture 39 of FIG. 4b is replaced by circular outputaperture 39. Advantageously, circular output apertures may provide moreaxially symmetric directionality than hexagonal elements. Further, inthe present embodiments the small size of the optical elements 1 meansthat the detailed structure of the output apertures may not be easilyresolved by observers, so that the output aperture of the whole array ofapertures 39 appears substantially uniform and thus has improvedcosmetic quality by way of comparison with macroscopic light emittingelement arrangements.

FIG. 17 shows in plan view the optical element array structure 41 ofFIG. 3b wherein the relative position of each structure 54 is differentfor optical elements 1 of the array, with structures 54, 138, 140, 142,144, 146, 148 with different relative positions for a single rosette.Such an embodiment advantageously averages out over the array the lossof reflectivity in the area around the pillar so that the combinedoptical output is substantially uniform. Thus the optical elementelectrodes 56 comprise a substantially linear feature 59 and theorientation of one first optical element electrode linear feature (forexample with structure 140) is different to the orientation of at leastone other first optical element electrode linear feature (for examplewith structure 142).

FIG. 18 shows an arrangement in which four light emitting elements 42comprising LEDs 150, 152, 154, and 156 (shown in more detail in FIG. 19below) provide light emitting sub-elements, and are positioned in theinput aperture 37 of each optical element. Such an arrangement providescompensation for short circuit loss of a single element during thelifetime of the element. FIG. 19 shows a detailed arrangement for theconnections to the LEDs in FIG. 18. At least one optical element 1 ofthe optical element array structure 41 of FIG. 3b is aligned with atleast two light emitting sub-elements. This provides some LED redundancyin the event of device failure. When controlled from a constant currentsupply, a string of LEDs produces a defined light output. If one of theLEDs 150, 154, 156 fails short circuit, the voltage drop of therespective LED is lost, but for a constant current supply the currentthrough the remaining LEDs remains the same as opposed to increasing aswould have happened with a constant voltage supply. Nevertheless thelight output is reduced by the short circuit failure of one LED. Innormal operation, active device 168 for example a transistor is on,effectively shorting LED 152 so that it does not emit. When shortcircuit failure of one of the other LEDs (150,154, 156) is detected,then active device 168 is turned off which provides LED 152 to turn onand thereby restoring the overall output to the pre-failure value. Anactive semiconductor device such as transistor 168 is arranged toprovide switching of at least one of the light emitting sub-elements.Other active devices such as triacs, thyristors or integrated circuitscan be used in cooperation with the light emitting elements.

Electrode layers may be formed on optical elements 1 as described in theillustrative embodiments of FIGS. 20 and 21. FIG. 20a shows in plan viewan array of optical elements 400 comprising an input aperture 402 and anelectrode support structure 404. FIG. 20b shows a mask 406 used to formelectrode pattern on the array of FIG. 20a comprising aperture regions408 and shielding regions 410. FIG. 20c shows the optical elements 400after formation of electrode 412 comprising light emitting element 42contact region 414 and backplane contact region 416. As shown in FIG.20d in cross section, metal material 417, such as aluminium, gold orIndium Tin Oxide (ITO) is deposited for example sputtered onto thesurface of the mask and is transmitted through apertures in the mask toprovide electrode 412. Advantageously such an arrangement can provide ahigh precision of electrode alignment to optical structures.

FIG. 20e shows one optical element 400 of an array of optical elementson which a metallic coating 418 is formed. In a material removal step, aregion of the opaque metal material is removed through a coating such asa photoresist coating and etch steps (as well known in the art), or maybe by means of laser ablation for example. As shown in FIG. 20f , theregion of removed material may be arranged to provide a transparentregion 420 for light transmission from the light emitting element and anelectrical isolation region 421 so that the contact between the lightemitting element and the backplane is through electrode 422.Advantageously the whole of the optical element 400 surface can beconveniently pre-coated with metal to provide both reflection andelectrical connection properties.

FIG. 20g shows an array of the elements of FIG. 20f in cross section.FIG. 20h shows an alternative embodiment in which the material 418 is atransmissive conductive material such as ITO. After a metal removalstep, as shown in FIG. 20i , an electrical isolation region 423 and aconnecting electrode region 424 are formed. Advantageously, a largecontact area to the light emitting element is provided to reduce therequired alignment precision of the electrode to the light emittingelement.

FIG. 21a shows a further method to form the electrode regions. An arrayof optical elements 400 comprising supporting material 101 isselectively over-coated by means of a printing process such as ink jet(not shown) or a coating roller 425 with a conductive material 426 suchas a conductive ink, to form electrode 412. In FIG. 21b as similararrangement is used to provide electrode 412 where the structure 404provides a platform for the coating roller and conductive material 426.

FIG. 21c shows a further method to form the electrode regions. Array ofoptical structures 400 is coated with a metal layer and then a material428 such as a photoresist or other etch resist material is selectivelyover-coated on the array to provide coated regions 430. The opticalelement is then etched and the material in regions 430 removed toprovide electrodes 432 as shown in FIG. 21 d.

An electronic control apparatus for an illumination apparatus may beprovided wherein respective electrodes are arranged for connecting atleast two light emitting elements of the plurality of light emittingelements. The electrical connection apparatus for the arrays of lightemitting elements of the present embodiments, which may be onedimensional or two dimensional arrays, may comprise several differentarrangements. Two or more of the LEDs 300 may be connected in parallelbetween common electrodes 301 and 302 as shown in FIG. 22. Lightemitting diodes are shown with output light 299 emission. Electrodes 301or 302 may take the form of a sheet electrode, 303. This requires alow-voltage high-current supply, and this arrangement works best if allthe individual LEDs are very well matched electrically. This arrangementis vulnerable to LED short circuit failure, but can tolerate opencircuit failure. Thus respective electrodes are arranged for connectinga plurality of light emitting elements in parallel.

FIG. 23 shows that two or more of the LEDs 300 may be connected tocommon electrode 302 which may take the form of a sheet electrode 303.The common electrode may be the anode or the cathode (shown). For a twodimensional array of n×m LEDs (where n and m are integers) this may bedriven by n×m current sources (not shown) each connected to each of anelectrode 304 of respective LED 300. Alternatively each LED can have aseries resistor (not shown) so that when the all the resistors areconnected together to a constant voltage supply (not shown) theresistors promote current sharing. The resistors associated with eachdevice may be integrated in the LED structure or external for example asshown as element 66 in FIG. 3. The function of a resistor for each LEDmay also be implemented by a uniform resistive layer (not shown), termeda ballast layer, between the LED electrodes and a common electrode.

FIG. 24 shows LEDs 300 connected in series strings 310, each of whichmay be driven by a current source (not shown), and connected by means ofelectrodes 305, 307. Thus respective electrodes are arranged forconnecting a plurality of light emitting elements in seriesdirectionally to form a string. In series directionally means thecathode of one device is connected to the anode of the next device inseries. This arrangement also reduces the number of current sourcescompared to FIG. 23 and means that the current source may operate athigher voltage. Each string still functions if an individual LED failsshort circuit. An open circuit failure disables only the string it isin. If required open circuit failures of an individual device can beprevented from disabling the whole string at the cost of incorporatingOpen Circuit Protectors (not shown) in parallel with the LED to beprotected. Suitable protectors include the PLED family marketed byLittlefuse (Chicago, Ill.). To reduce components count, one Open CircuitProtector can be configured to protect for example two LEDs in series,however if only one LED fails, both will be dark. Alternatively a zenerdiode (not shown) can be configured in anti-parallel with each LED, orLED pairs. The zener voltage should exceed the forward voltage drop ofLED(s) it is protecting. LEDS may be protected from Electro-StaticDischarge (ESD) damage by incorporating ESD protection devices such asESD diodes. These devices can be configured in parallel with one or moreLEDs or connected at the external electrodes of the LED array. Theindividual strings 310 of LEDs 300 of FIG. 24, which may for examplecorrespond to a row of n devices in the LED array, may themselves beconnected in series for example by electrodes 309 to further reduce thenumber of drive circuits, or to raise the operating voltage to be morecompatible with the available supply for example as in FIG. 25. Theelectrical arrangement discussed above can apply to a spatiallydifferent topology of the LED array for example hexagonal or square. TheLEDs connected in a string need not be adjacent and may be spatiallyseparated to promote optical uniformity in the event that a particularstring fails.

The drive circuit for the plurality of light emitting elements maycomprise at least one current source.

Current sources may be multiplexed to multiple strings of light emittingelements as shown schematically in the illustrative embodiment of FIG.26. In operation current source 318 is connected to group of 4 parallelstrings 330 of LEDs. Current sources 320, 322 etc. are similarlyconnected to strings 332, 334. In a first illumination phase (phi 1) thefirst of the 4 parallel strings in each of groups 330, 332, 334 isconnected to the respective current sources and is turned on (e.g.grounded by means of transistor 324). In phase two, the current sourcesare used to control the second string in each group. At least onecurrent source 322 may thus be multiplexed to multiple strings of lightemitting elements 42. This system has the advantage of reduced number ofcurrent sources. Multiplexing the current sources also reduces thenumber of electrical connections that are needed to the array

The array may also have some LEDs connected in arrangements intended forAC operation. FIG. 27 shows an AC power source 341 and a basic opposedstrings 340, 342 each comprising one or more LEDs 300. Each stringilluminates on opposing polarity (usually half cycles) of the ACwaveform. The string may contain enough devices to make the totalforward diode voltages suitable to the AC voltage available. If thecurrent is limited, for example by a resistor (not shown), then thecircuit has some tolerance to short circuit failures of LEDs. Unlessprotected open circuit failure of a LED will disable whichever of thestring 340, 342 the failed device is in. The strings may also furthercomprise a connecting link 344 as shown in FIG. 28. A short circuitfailure in any LED also disables the LED electrically in parallel.Disadvantageously this arrangement is not tolerant to open circuitfailure.

Some or all of the devices of the array may be configured as one or morebridge circuits e.g. half wave bridge circuits (not shown) or full wavebridge circuits as illustrated in FIG. 29. The arms of the bridgecontain light emitting rectifying diodes. This circuit has the advantagethat the centre string 346 emits on both positive and negative cycles ofthe AC power source 341. Sufficient light emitting diodes are needed inthe arms 348 of the bridge (two are shown for illustration in each arm)to sustain the reverse voltage of the AC waveform from the source 341.For a typical AC waveform, these LEDs in the arms 348 only emit on halfthe cycles.

FIG. 30 illustrates another approach where the bridge is provided by nonlight-emitting rectifier diodes 350 in each arm that have a high reversevoltage tolerance and preferably a low forward voltage for examplesilicon diodes. This embodiment provides all the LEDs 300 to emit onpositive and negative cycles of the AC source 341. Such a silicon diodebridge is conveniently incorporated with the array embodiments, forexample element 66 in FIG. 3.

The control circuitry associated with the above embodiments may alsoincorporate one or more of features such as power factor correction,current limit, over temperature and over voltage protection, as is knownin the art. The control circuitry may also incorporate and Infra Red orwireless RF receiver to provide control of the functions of the lamp.

Strings of LEDs may be used for high voltage DC operation withoutneeding a bridge circuit. Any reverse voltage including possibletransients across the LED string 346 may be clamped with for example asilicon diode 350 and a high value (e.g. one mega-ohm) resistor 352 asshown in FIG. 31.

Some or the entire LED array may be connected as a cross point matrixFIG. 32. In this case the same electrode (say the anode) of all LEDdevices 300 in a row e.g. 306 are connected together, and the other LEDelectrodes (cathodes) in a column e.g. 304 are all connected together.When all devices are connected to their respective rows and columns,this produces a light source like a matrix display, which can beaddressed one row at a time. For an n×m array only m fast, high powercurrent sources 308 are needed as typically each device is illuminatedfor 1/n of the time. With suitable control this system can be arrangedto function as a display or as a signalling device as well as provideillumination. The signalling function may be performed at such a speedand/or wavelength as to be unnoticeable to humans. The plurality oflight emitting elements can thus be connected in an addressable array.

FIG. 33 shows that a transistor 360 can be used to short circuit thevoltage across a LED 300 so that ordinarily it does not operate. Ifgreater light output is needed, for example if another element hasfailed, then the transistor may be switched to high resistance and LED300 is now free to operate. The failure of a device may be detected bymeans of sense resistor 362 and circuitry block 364. Different stringsor parts of the array may be turned on or off in order to facilitatedimming and or lumen maintenance. Different colour LEDs may be turned onor off to facilitate a change in colour temperature or a change incolour temperature when dimming the light.

FIG. 34a shows a further embodiment for providing an array of electrodeconnections. Substrate 500 may comprise the array of optical elementssuch as item 41 in FIG. 9 or may be a plane substrate such as a glass,silicon, metal or ceramic substrate which may further compriseadditional elements such as electrodes and heat spreaders. An array oflight emitting elements 502 is formed on the substrate 500 and in afirst step, a shadow mask 504 is provided in alignment with the array oflight emitting elements 502. The mask 504 comprises an array ofapertures 503 with size that is greater than the size of the electroderegion to be provided on the upper surface of the light emittingelements 502. The mask may comprise for example a high melting pointmetal or a polymer material such as polyimide.

In a second step as shown in FIG. 34b , a coating 506 is formed on thesurface of the light emitting elements 502 and mask 504. The coating 506may comprise metal or dielectric materials suitable for providingelectrical connection to the upper surface of the light emittingelements 502 and insulation from surrounding electrical features. Thecoating may comprise a stack of materials of required thicknessincluding but not limited to titanium, palladium, aluminium, gold,silver, indium, nickel and alloys thereof. The coating 506 may be formedby evaporation, sputtering, chemical vapour deposition or other knownmethods. Advantageously, after forming the coating 506, the material ofone or more of the coatings 506 deposited on mask 504 may be recycled.Typically the light emitting elements 502 of the present embodimentscomprise relatively small devices, for example 100 micrometers widthwith spacing of for example 1 mm or more. Such an arrangement means thatthe area coverage of the light emitting elements may be less than about1% of the total area on which the coating is formed. In this manner, thecoating materials 506 may be recycled to reduce cost.

After the deposition step of FIG. 34b , the thickness of the coatingdeposited through the shadow mask may be subsequently increased by anelectro-deposition or plating process using the regions depositedthrough the mask as seed layers.

In a third step a lithographically patterned array of photoresist 508may be formed on the surface of the coating 506 and light emittingelements 502 as is well known in the art. In a fourth step, etching isused to selectively remove part of the coating 506 so as to provide asmall electrode region 507. In this manner, the high precision and smallsize of photolithographic electrodes can be combined with the recyclingcapability of the lower precision shadow mask technology. Advantageouslysmall electrodes that provide high light output can be provided at lowcost. Further, the light emitting elements operate in a VTFconfiguration enabling higher current density with high efficiency.

FIGS. 35a-c show an alternative method for forming an array ofelectrodes comprising a ‘lift-off’ step. In a first step as shown inFIG. 35a , a patterned photoresist layer 510 comprising aperture regions511 is formed on the surface of the substrate 500 and light emittingelements 502. As shown in FIG. 35b , a coating 506 such as a stack ofmetal layers is formed on the photoresist for example by evaporation orsputtering. In a third step as shown in FIG. 35c a known photoresistlift off technique is provided to remove the coating outside the desiredelectrode region 507. The metal of coating 506 can be recovered from thelifted off material and advantageously recycled.

FIGS. 35d-f show an alternative method for forming an array ofelectrodes. In a first step as shown in FIG. 35d , a substantiallyuniform layer 512 is provided on the surface of the substrate 500 andlight emitting elements 502. The layer 512 may comprise for example apolyimide layer. In a second step as shown in FIG. 35e apertures 514 areprovided for example by means of photolithography or laser patterning.In a further step as shown in FIG. 35f , electrodes may be patterned onthe surface, for example by means of an evaporator and shadowmask (notshown). FIG. 35g-i show a further method for forming an array ofelectrodes. In a first step as shown in FIG. 35g , light emittingelements are arranged on an electrode array 518 and the layer 512, forexample polyimide provided. As shown in FIG. 35h , via holes 520 areformed in the layer 512, for example by means of photolithography orlaser patterning. As shown in FIG. 35i , electrodes are patterned on theupper surface of layer 512 to provide a VTF type electrode connection.The processes of FIGS. 35a-i may be applied to planar substrates or tooptical element arrays to provide first and second electrode arrays.

FIGS. 36a-36d show a further method to provide an array of lightemitting elements. In FIG. 36a , a semiconductor support substrate 520is provided with an array 522 of light emitting elements formed on itssurface separated by gaps 526 and arranged with a first adhesivesubstrate 524. For example the semiconductor support substrate 520 maybe sapphire, the light emitting elements may be gallium nitride and thegaps 526 may be formed by laser scribing or other known scribing,etching or ablation techniques. Ultraviolet electromagnetic radiationbeams 529, 530, 531 from a homogenised excimer laser are used toilluminate patterned regions 528 in alignment with some of the lightemitting elements of the array 522. Light is transmitted through thesubstrate 520 and by illumination with a short pulse of light,decomposition of the semiconductor material close to the interface ofthe substrate 520 achieves a loss of adhesion of the light emittingelement to the substrate 520. For example, gallium nitride illuminatedwith a 30 nanosecond pulse of energy approximately 1 J/cm2 disassociatesthe gallium nitride to provide gallium metal and nitrogen gas.

After exposure in a separation step as shown in FIG. 36b , the sandwich520, 522, 524 may be heated above the melting point of gallium toachieve selective detachment of the light emitting elements of the array522 from the substrate 520. On illumination of the respective lightemitting elements of the array 522, transfer of an array of separatedlight emitting elements 532 to adhesive substrate 524 is thus achievedby means of laser lift off while the remaining light emitting elementsof the array 522 remain attached to the substrate 520.

The array 522 may advantageously be in contact with an adhesivesubstrate 524 as shown in FIG. 36c . The adhesive substrate 524 mayadvantageously comprise a surface with weak adhesive properties capableof providing a temporary bond to the light emitting elements after thelaser lift off step. A suitable material for the adhesive substrate maybe a cross linked polydimethylsiloxane, PDMS that may be free standingor may be formed as a pre-cured adhesive layer 525 on a rigid orsemi-rigid substrate 523. The support substrate may be rigid such asglass, or may be for example a flexible polymer sheet. Alternatively thePDMS may be cured in contact with the array 522 of light emittingelements with or without a backing substrate.

The substrate 524 may comprise other adhesive materials with weakadhesive properties such as waxes or pressure sensitive adhesives orlayers 525 with a sparse distribution of adhesive regions on a scalesmaller than the light emitting elements achieving a low adhesive forceand low separation energy for subsequent substrate separation steps. Asshown in FIG. 36d , an adhesive layer may comprise regions 527 ofadhesive material 525 that may be aligned with the respective lightemitting elements during the laser lift off step. Alternatively as shownin FIG. 36e , the layer 525 may comprise surface relief regions 529 ofadhesive material. The embodiments of FIGS. 36d and 36e advantageouslyreduce the adhesion of the substrate 524 to the elements that are notremoved in the laser lift off step, or the adhesion of the layer 525 tosubsequent attachment substrates.

Advantageously, the adhesive force of the substrate 524 to theselectively removed light emitting elements may hold the selectivelyremoved light emitting elements from the laser lift off step whilereleasing from light emitting elements on the semiconductor substrate520 that were not exposed to laser illumination.

The adhesive material 525 may advantageously comprise a flexible layerarranged to conform with the surface of the semiconductor supportsubstrate 520 and array 522 of light emitting elements. The substrate520 and array 522 may be formed from materials with different thermalexpansion coefficients, so that at room temperature the array 522 iswarped. A rigid support substrate 523 may not be conveniently arrangedin contact with all elements of the array 522, whereas a flexiblesupport substrate 523 can conform to the surface. Alternatively gaps 526may be arranged to relieve the stress in the layer 522 thus enabling aplanar substrate 520 and a rigid substrate 523 to be provided.

The separation s1 of the light emitting elements from the semiconductorsupport substrate 520 is substantially the same as the separation on theadhesive substrate 524. The separation s1 may advantageously besubstantially the same as the separation of the input apertures of thearray of optical elements providing uniform illumination across largearrays of components, thus enabling mothersheet substrate processing. Amothersheet comprises a light emitting element support substrate ofextended size, thus enabling many light emitting elements to beprocessed in parallel. Further the mothersheet area may be of sufficientsize so that many illumination apparatuses can be processed in parallel.For example, an illumination apparatus may achieve a 1000 lm output, andthe mothersheet may be of sufficient size to achieve parallel processingoften or more such devices in parallel prior to a singulation step.Advantageously such a mothersheet substrate processing approach canproduce significant reduction in illumination apparatus cost.

In a further step as shown in FIG. 36f , second regions of the array 522are transferred from the semiconductor support substrate 520 onto asecond adhesive substrate 534 to provide a second array 536 of separatedlight emitting elements with separation s1 as shown in FIG. 36 g.

As shown in FIG. 36h in plan view, multiple substrates including 524 and534 may be aligned onto a mothersheet support substrate 535 to producean extended array of light emitting elements from which manyillumination elements may be formed. Substrate 535 may comprise forexample an optical element array structure 41 (in FIG. 9) comprisingoptical elements 1 or may be a plane substrate such as a glass orceramic substrate which may further comprise additional elements such asheat spreaders and electrodes. Advantageously such an arrangementachieves the alignment of multiple arrays on a single substrate. Theadhesive substrate 524 may comprise a flexible substrate that can bendin conformity with both a semiconductor support substrate 520 andsubstrate 535. Advantageously, such an arrangement achieves arrays oflight emitting elements to be extracted from warped wafers 520 andapplied to flat substrates 535. Advantageously the arrays of lightemitting elements 532, 536 may be aligned with lithographic precision sothat the composite arrays on the substrate 535 achieve high precision ofalignment with the respective optical elements.

The gaps 526 of FIG. 36a may be provided by means of laser scribing,etching partial sawing or other know separation techniques.Alternatively, as shown in FIG. 36i , the array 522 of light emittingelements may be provided with no pre prepared gaps, and is provided inlayers (for example n doped and p doped layers). An optional supportlayer 521 which may be patterned may be formed on the array 522. Theultraviolet electromagnetic radiation beam illumination 529, 530, 531may be arranged so as to provide separation of the elements defined bythe size of the beam providing sparse array separation as shown in FIG.36j . The step in which the gap 526 (as shown in FIG. 36a ) is formed iseliminated and advantageously cost is reduced. On laser exposure of thelayer 522, defects such as cracks in the emitting layer may propagate,damaging the removed light emitting elements.

Thus a method of manufacturing an illumination apparatus may comprisethe steps of: forming a monolithic array of light-emitting elements on asupport substrate in a continuous layer; selectively removing aplurality of light-emitting elements from the monolithic array in amanner that preserves the relative spatial position of the selectivelyremoved light-emitting elements; wherein the monolithic array oflight-emitting elements are illuminated by a plurality of shaped laserbeams; wherein the plurality of light-emitting elements that areselectively removed from the monolithic array are selected such that, inat least one direction, for at least one pair of the selectively removedlight-emitting elements in the at least one direction, for eachrespective pair there is at least one respective light-emitting elementthat is not selected that was positioned in the monolithic array betweenthe pair of selectively removed light-emitting elements in the at leastone direction. A patterned support layer may be formed on the pluralityof light emitting elements.

Thus a method of manufacturing an illumination apparatus may comprise:forming a monolithic array 522 of light-emitting elements made of aplurality of layers on a substrate 520, the light emitting elements 532being inter-connected in the layers they are formed in; selectivelyilluminating a plurality of the light emitting elements 532 with anillumination 529, 530, 531 that separates, at least to an extent, theselected light emitting elements 532 from the substrate 520; theillumination 529, 530, 531 further breaking the connection in the layersbetween each selectively illuminated light emitting element 532 and theother light emitting elements; removing the illuminated light-emittingelements 532 from the monolithic array in a manner that preserves therelative spatial position of the removed light-emitting elements 532;wherein the plurality of light-emitting elements 532 that areselectively illuminated and removed from the monolithic array areselected such that, in at least one direction, for at least one pair ofthe selectively illuminated and removed light-emitting elements in theat least one direction, for each respective pair there is at least onerespective light-emitting element that is not selected that waspositioned in the monolithic array between the pair of selectivelyilluminated and removed light-emitting elements 532 in the at least onedirection. Further a patterned support layer 521 may be formed on theplurality of light emitting elements 532.

Advantageously, patterned or unpatterned support means 521 can beprovided on the surface of the array 522 to reduce damage during thelaser processing step and to provide uniform size of extracted materialfrom the array 522. The layer 521 may be a metal layer and may form partof the electrode structure of the device or may be some other layer suchas a polymer stabilisation layer that may be removed in subsequentprocessing steps. The edges of the light emitting elements may becleaned, for example by means of a laser writing or selective etch step.

Gallium nitride LEDs are typically grown with the n-doped side incontact with the wafer (n-down) with the p-doped side uppermost (p-up).The embodiment of FIG. 36h provides n-down LEDs on the substrate 535wherein the n doped side is in contact with the substrate. Such anarrangement requires a transparent current spreading electrode to beformed on the p doped side of the chip which reduces the optical outputof the chip. It is advantageous to provide arrangements wherein the pdoped side of the chip is coated with a highly reflective conductiveelectrode and is positioned in contact with the substrate (p-down). Thehigher conductivity of the n doped side of the LED means that atransparent current spreading electrode is not necessary and thusincreases optical output. FIGS. 37a-37d show one method to achieve ap-down arrangement. After the step of extraction of the array 532 ontothe receiver substrate 524 as shown in FIG. 36b , a material 540 isapplied to the surface of the substrate 524 and array 532 as shown inFIG. 37a . The material 540 may for example be a photoresist orpolyimide material. A further substrate 538 may be provided to supportthe material 540. After processing of the material 540, for example bymeans of heat or by UV illumination, the receiver substrate 524 isremoved as shown in FIG. 37b , achieving embedding of the array 532 inthe material 540 with the p-doped surfaces exposed. Advantageously, theadhesive force between the adhesive material 525 of the adhesivesubstrate 524 to the light emitting element array 532 is lower than theadhesive force between the material 540 to the array 532. The array 532is then brought into contact with the substrate 535 which may compriseheat spreading, electrode and light reflecting elements 542 as shown inFIG. 37c . Advantageously, the light emitting elements 532 areincorporated into a material 540 capable of withstanding processtemperature required for formation of solder joint to the heat spreaderand electrode elements 542. After soldering the material 540 andsubstrate 538 is removed for example by immersion in a suitable solventor by peeling at an elevated temperature as shown in FIG. 37 d.

Similarly a further light emitting element array 536 may be transferredto a separate region of the substrate 535. Such a process advantageouslypreserves the separation of the light emitting elements of therespective arrays while providing p-doped side of the light emittingelements in contact with the substrate electrodes.

Thus a method of manufacturing an illumination apparatus comprises thesteps of forming a monolithic array 522 of light-emitting elements;selectively removing a plurality of light-emitting elements from themonolithic array 522 to a first adhesive substrate 524 in a manner thatpreserves the relative spatial position of the selectively removedlight-emitting elements; transferring the plurality of light emittingelements from the first adhesive substrate 524 to a second adhesivesubstrate 538, 540 in a manner that preserves the relative spatialposition of the selectively removed light-emitting elements wherein theadhesive force of light emitting elements to the second adhesivesubstrate 538, 540 is greater than the adhesive force of the lightemitting elements to the first adhesive substrate 524; transferring theplurality of light emitting elements from the second adhesive substrate538, 540 to a substrate 535 in a manner that preserves the relativespatial position of the selectively removed light-emitting elementswherein the adhesive force of the light emitting elements to thesubstrate 535 is greater than the adhesive force of the light emittingelements to the second adhesive substrate 538, 540; wherein theplurality of light-emitting elements that are selectively removed fromthe monolithic array 522 are selected such that, in at least onedirection, for at least one pair of the selectively removedlight-emitting elements in the at least one direction, for eachrespective pair there is at least one respective light-emitting elementthat is not selected that was positioned in the monolithic array betweenthe pair of selectively removed light-emitting elements in the at leastone direction.

Thus a method of manufacturing an illumination apparatus; comprises:forming a monolithic array 522 of light-emitting elements; selectivelyremoving a plurality of light-emitting elements 532 from the monolithicarray 522 by adhering them to a first adhesive substrate 524 in a mannerthat preserves the relative spatial position of the selectively removedlight-emitting elements 532; transferring the plurality of lightemitting elements from the first adhesive substrate 524 to a secondadhesive substrate 538, 540 in a manner that preserves the relativespatial position of the selectively removed light-emitting elements 532;transferring the plurality of light emitting elements 532 from thesecond adhesive substrate 538, 540 to a support substrate 535 in amanner that preserves the relative spatial position of the selectivelyremoved light-emitting elements 532; wherein the plurality oflight-emitting elements 532 that are selectively removed from themonolithic array are selected such that, in at least one direction, forat least one pair of the selectively removed light-emitting elements 532in the at least one direction, for each respective pair there is atleast one respective light-emitting element that is not selected thatwas positioned in the monolithic array between the pair of selectivelyremoved light-emitting elements in the at least one direction. Theadhesive force of light emitting elements 532 to the second adhesivesubstrate 538, 540 may be greater than the adhesive force of the lightemitting elements 532 to the first adhesive substrate 524. The adhesiveforce of the light emitting elements 532 to the support substrate 535 isgreater than the adhesive force of the light emitting elements 532 tothe second adhesive substrate 538,540. The support substrate maycomprise an array of optical elements 1 and the array of light emittingelements 532 is aligned with the respective optical elements 1. Thesupport substrate 535 may comprises a planar substrate wherein the arrayof light emitting elements 532 is aligned with an optical element arraystructure 41 comprising an array of optical elements 1.

Errors due to scratches, pits, epitaxial errors and other effects may bepresent on the epitaxial wafer prior to extraction of individual lightemitting elements. FIG. 38a shows an embodiment in which wafer defectsare present in light emitting elements of a monolithic array 522 and arecharacterised. For example, an element sensor 543 is used to determinethe location of individual ‘passed’ light emitting elements 546 thathave characteristics below a threshold tolerance of a functionalcriterion and ‘failed’ light emitting elements above a thresholdtolerance of a functional criterion. The element sensor 543 may providefor example a functional criterion that comprises a distribution ofoutput wavelength across the array and the defects may be due to varyingthicknesses of epitaxial layers that result in differences in outputwavelength. Passed devices 546 may be for example those with deviationfrom the target wavelength of less than or equal to +/−2 nm while faileddevices 544 may have a deviation from the target wavelength of greaterthan +/−2 nm. Alternatively the element sensor may measure a functionalcriterion comprising surface defect characteristics or may determineelectrical characteristics of the light emitting elements. An areasensor 547 may provide measurements from groups 543 of light emittingelements, such that light emitting elements in groups 543 are classed aspassed or failed light emitting elements. Pass distributions comprisingthe location of passed light emitting elements and fail distributionscomprising the location of failed light emitting elements may thus beprovided. Fail distributions will typically comprise those elements thatare not in the pass distribution. It is desirable that the lightemitting elements 544 in the fail distribution are not incorporated ontothe substrate 500 as they may cause for example at least reducedbrightness, incorrect colour, short circuit or open circuit.

As shown in FIG. 38b , in the lift off step, the patterned UVillumination is modified so that beam 530 is absorbed, reflected ordiffused by a feature 537 formed on the opposite side of thesemiconductor support substrate 520 to the epitaxial layer comprisingarray 522 of light emitting elements. Feature 537 may for examplecomprise a deposited region of absorbing material in alignment with theelement 544 that may be formed by an addressable printing method such asinkjet printing, a structured diffusing surface produced by laserprocessing or a patterned metal formed by a deposition method. Onillumination, beam 530 is absorbed, diffused or reflected while beams529, 531 are transmitted. If the power density at the surface of theelement 544 with the semiconductor support substrate 520 falls below athreshold, then element 544 will not be lifted off and will remainattached to the semiconductor support substrate 520 as shown in FIG. 38cwhile the passed light emitting elements 546, 548 are transferred ontothe substrate 500 and leaving an unfilled element 547 as shown in FIG.38 d.

In further steps shown in FIGS. 38e-38g , regions of the substrate 500with missing light emitting elements are filled by means of extractionof an array 558 of light emitting elements from another part of thewafer or indeed a second wafer 550 and array of light emitting elements552. FIG. 38e shows the patterned laser lift off step and FIG. 38f showsthe separated elements on the adhesive substrate 554. Adhesive substrate554 is aligned with substrate 500 and array of elements 542 so as toprovide an array of light emitting elements 546, 558 from respectivefirst and second wafers on the substrate 500 as shown in FIG. 38 g.

A method of manufacturing an illumination apparatus thus comprises:forming a first monolithic array 522 of light emitting elements;determining a first plurality of the light emitting elements 546, 548which pass a functional criterion; determining a second plurality of thelight emitting elements 544 which fail the functional criterion;selectively removing a plurality of the passed light emitting elements546, 548 whose relative positions in the first monolithic array 522correspond to desired relative positions in a desired non-monolithicarray of light emitting elements, the selectively removing beingperformed in a manner that preserves the relative spatial position ofthe selectively removed passed light-emitting elements 546, 548; whereinthe plurality of passed light-emitting elements 546, 548 that areselectively removed from the monolithic array 522 are selected suchthat, in at least one direction, for at least one pair of theselectively removed passed light-emitting elements 546, 548 in the atleast one direction, for each respective pair there is at least onerespective light-emitting element that is not selected that waspositioned in the monolithic array between the pair of removed passedlight-emitting elements in the at least one direction; and forming anon-monolithic array of light-emitting elements with the selectivelyremoved passed light-emitting elements 546, 548 in a manner thatpreserves the relative spatial position of the selectively removedpassed light-emitting elements; by virtue of which in the formednon-monolithic array of light emitting elements desired relativepositions of the desired array that correspond to passed light emittingelements in the first monolithic array are occupied by passed lightemitting elements 546, 548 and desired relative positions of the desiredarray that correspond to failed light emitting elements in the firstmonolithic array are left unoccupied. Further light emitting elements558 may be added to the formed non-monolithic array of light emittingelements in unoccupied desired relative positions of the desired array.The further light emitting elements 558 may be from a second monolithicarray 552 of light-emitting elements that is different to the firstmonolithic array 522 of light-emitting elements. The further lightemitting elements 558 may be from the first monolithic array oflight-emitting elements. The further light emitting elements 558 may belight emitting elements which have been determined as passing thefunctional criterion. A light intensity reduction region 537 may beformed on a surface of the monolithic array support substrate 520aligned with the second plurality of light emitting elements 544.

Advantageously, elements with known poor performance are not present inthe transferred array, improving the yield and achieving a reducedrequirement for testing of the final light emitting element array on thesubstrate. Such a method can therefore reduce the cost and improve theperformance of the substrate array. In some applications, particularlythose requiring observers to look directly at the light engine, it maybe desirable that all of the light emitting elements are functional toavoid dead spots in the output illumination. In this embodiment, furtherprocessing steps may be undertaken to prevent defects in the array 552being transferred to substrate 500 using further wafers.

Alternatively as the final devices on the substrate 535 contain lightemitters from a wide area of wafer, depending on the yield statistics itmay be advantageous not to fully test the wafer and to transfer somedefective or even all devices. The averaging effect across the mothersheet means this may achieve satisfactory performance. Alternativelyonly emitters identified open circuit (non emitting) may be held backfrom transfer.

Thus a method of manufacturing an illumination apparatus may comprisethe steps of forming a first monolithic array 522 of light-emittingelements; characterising the first monolithic array of light emittingelements to provide a pass distribution and a fail distribution of lightemitting elements; selectively removing a plurality of passedlight-emitting elements 546 from the first monolithic array 522 in amanner that preserves the relative spatial position of the selectivelyremoved passed light-emitting elements 546; forming a non-monolithicarray of light-emitting elements with the selectively removed passedlight-emitting elements 546 in a manner that preserves the relativespatial position of the selectively removed passed light-emittingelements; wherein the plurality of passed light-emitting elements thatare selectively removed from the first monolithic array 522 are selectedsuch that, in at least one direction, for at least one pair of theselectively removed passed light-emitting elements in the at least onedirection, for each respective pair there is at least one respectivelight-emitting element that is not selected that was positioned in thefirst monolithic array between the pair of passed selectively removedlight-emitting elements in the at least one direction; selectivelyremoving a second plurality of light-emitting elements 558 from amonolithic array 552 of light emitting elements wherein the secondplurality of light-emitting elements 558 are arranged with at least partof the fail distribution in a manner that preserves the relative spatialposition of the selectively removed second plurality of light-emittingelements 558; interspersing the second plurality of light-emittingelements 558 with the first plurality of passed light-emitting elements546 to provide a corrected non-monolithic array of light emittingelements; and aligning the corrected non-monolithic array oflight-emitting elements with an array of optical elements.

The method may further comprise the steps of forming a light intensityreduction region 537 on a surface of the monolithic array supportsubstrate 520 aligned with the respective fail distribution of lightemitting elements.

As shown schematically in FIG. 39a , open circuit errors may occur forexample due to attachment errors between the light emitting elements560, 562, 564 and electrode arrangement 566. Additional circuitry 568can be incorporated in the region of the light emitting elements so thatin the case of a diagnosed error, a conductive material can be appliedin the region 570. For example, testing may demonstrate that elements560 and 562 are operating correctly whereas element 564 is open circuit.In this embodiment, a solder patch is applied to the region 570 to shortcircuit the region of the light emitting element. This embodimentachieves a greater reliability for light emitting elements connected ina series string. As shown in FIG. 39b a similar defect correction can beachieved by applying a conductive layer (e.g. solder) 562 directly overthe light emitting element 564.

FIG. 40 shows in plan view a string of light emitting elements 560, 562,564 connected by means of metallic heat spreaders 574, p-electrodesolder region 576, n-electrode 578 and insulator 580. If element 564 isdiagnosed as faulty, a conductive material can be applied in the region584 to provide a short circuit so that the electrical string canadvantageously continue to operate for elements 560 and 562.

FIG. 41 shows in plan view an epitaxial wafer 586 used to form an arrayof light emitting elements. Epitaxial growth non uniformities provide avariation of emission wavelength and forward voltage characteristics forelements across the surface of the wafer. Light emitting elements canthus be binned (i.e. placed into groups with similar properties) basedon the region 588, 590, 592, 594, 596, 598 from which they originate onthe wafer. The extraction process of for example FIGS. 36a-h may be usedto extract a sparse array of light emitting elements from across theentire surface of the wafer 586. The extracted light emitting elementsare arranged as a sparse array extracted from the wafer rather than fromadjacent positions on the epitaxial layer on the wafer. For example, thelight emitting elements may have size of 100×100 micrometres on a pitchof 2×2 millimetres. Light emitting elements are thus extracted fromsubstantially all of the regions 588, 590, 592, 594, 596, 598 in eachextraction step.

The sparse array may then be assembled in alignment with other sparsearrays onto a support substrate 500 (which may be a large areamothersheet) as shown in plan view in FIG. 42a . Thus sparse arrays 601,603, 605, 607, 609, 611 are arranged together on substrate 500. Theproperties of the respective sparse arrays vary spatially across thewafer 586 and the spatial variation of properties are thus transferredto the support substrate 500. The orientation of sparse arrays 601, 603,605, 607, 609, 611 is shown in FIG. 42a as being the same. Theorientation of the extracted sparse arrays 601, 603, 605, 607, 609, 611may alternatively be varied to advantageously provide a mixture of binregions and so properties within any single illumination element.

After a singulation step, individual illumination element regions 606,608 (those that are used for example in a light engine for a singlelighting fixture) are extracted from the substrate after cutting alonglines 604, providing singulated illumination element regions 606, 608 asshown in FIG. 42b and FIG. 42c respectively. The singulation may bebefore or after alignment with optical elements and wavelengthconversion layers described below.

Respective illumination element regions 606, 608 may comprise differentportions of each of the respective bin regions 588, 590, 592, 594, 596,598. Alternatively, the illumination element regions 606, 608 maycomprise mixtures of regions from different wafers, for example achievedby arranging sparse arrays from different wafers on the substrate 500.

The integrated emission wavelength is an average of the emission fromeach of the elements within the respective illumination element regions606, 608. The integrated emission wavelength advantageously compriseslight from light emitting elements arranged in multiple bins and is thusan average value between the extremes of emission wavelength forindividual light emitting elements. The difference in integratedemission wavelength for illumination element regions 606, 608 willtypically be smaller than the total deviation of wavelength within asingle wafer, reducing light engine bin size and illumination elementcost.

By way of comparison, with standard pick-and-place extractiontechniques, individual light emitting elements with size for example 1×1millimetre are extracted from single regions of the wafer and thus havethe properties of the single region. Such light emitting elements thusdo not have the property averaging advantages of the presentembodiments. Advantageously, reduced bin size achieves a reducedvariation of illumination element properties, requiring less testing andhigher control of properties, thus reducing cost and improvingperformance.

Gallium nitride LEDs typically produce a blue output that is convertedto white light by means of a wavelength conversion material such as aphosphor. It would be desirable to further reduce the number of bins bytuning the wavelength conversion material to match the average emissionwavelength of the respective illumination element regions 606, 608. Asshown in FIG. 43, after preparation of the substrate 500 as shown inFIG. 42a , the substrate 500 may further comprise at least two differentphosphor coating regions 614, 615 tuned to the average emission of therespective illumination element regions 606, 608 respectively. Thus eachof the white light illumination elements fabricated from blueillumination element regions 606, 608 and respective aligned wavelengthconversion regions 614, 615 may have a small bin range. Advantageously,the emission wavelength, voltage and other properties of the lightengine can be produced in small bins thus further reducing cost.

The respective phosphor for the illumination element regions 606, 608may be provided after dicing of the substrate 500 and singulation of theillumination element regions 606, 608. Alternatively FIG. 44 shows anembodiment wherein a patterned phosphor layer is applied across thesubstrate 500 prior to dicing and singulation. In illumination elementregion 608, a phosphor coating layer 612 is applied to light emittingelements 610 after measurement of the combined spectral output acrossthe illumination element region 606. A sensor 617, such as a colorimeteror spectrophotometer is arranged to integrate the light from across therespective illumination element region and measure the combined spectraloutput of at least some of the light emitting elements 611. The expectedregion average white point may be determined by measuring the blue lightoutput from the light emitting elements 610 and determining the whitepoint that would be provided by a standard phosphor. This can then beused to provide the properties of a suitable matched phosphor layer 618spectral characteristic to achieve the desired target white point. Inillumination element region 608, a second phosphor layer 612 isprovided, with spectral characteristic tuned to the mean emissionwavelength of the light emitting elements 610. The phosphor may printedby means of a screen or stencil 620 and doctor blade 622 across therespective region. Alternatively the phosphors may be selectivelydeposited by an inkjet process. In this manner, high precision printingof individual phosphor coatings tuned to each of the individual lightemitting elements is avoided, thus decreasing cost for a small bin sizeand achieving higher performance.

Thus a method of manufacturing an illumination apparatus may comprisethe steps of forming a non-monolithic array of light-emitting elements611, 612 on a support substrate 500; measuring the spectral output of atleast some of the light-emitting elements 611 in a first region 606 ofthe support substrate 500; providing a first wavelength conversion layer618 in alignment with the respective light emitting elements 611 of thefirst region 606 arranged to provide a first region average white point;measuring the spectral output of at least some of the light-emittingelements 610 in a second region 608 of the support substrate 500;providing a second wavelength conversion layer 612 different to thefirst wavelength conversion layer 618 in alignment with the respectivelight emitting elements 610 of the second region 608 arranged to providea second region average white point; wherein the first and second regionaverage white points are the same.

Thus a method of manufacturing an illumination apparatus may comprisethe steps of forming a non-monolithic array of light-emitting elements611 on a support substrate 500; for at least some of the light-emittingelements 611 in a first region 606 of the support substrate 500,measuring their combined spectral output; providing a first wavelengthconversion layer 618 in alignment with the respective light emittingelements 611 of the first region 606, the spectral characteristic of thefirst wavelength conversion layer 618 being selected dependent upon themeasured combined spectral output from the measured light emittingelements 611 of the first region 606; for at least some of thelight-emitting elements 612 in a second region 608 of the supportsubstrate 500, measuring their combined spectral output; and providing asecond wavelength conversion layer 612 in alignment with the respectivelight emitting elements 610 of the second region 608, the spectralcharacteristic of the second wavelength conversion layer 612 beingselected dependent upon the measured combined spectral output from themeasured light emitting elements 610 of the second region 608.

A first region average white point may be provided by virtue ofproviding the first wavelength conversion layer 618 in alignment withthe respective light emitting elements 611 of the first region 606; asecond region average white point may be provided by virtue of providingthe second wavelength conversion layer 612 in alignment with therespective light emitting elements 610 of the second region 608, andwherein the first region average white point and the second regionaverage white point are thereby more similar than they would be if thetwo regions 606, 608 had been provided with a same wavelength conversionlayer. A first region average white point is provided by virtue ofproviding the first wavelength conversion layer 618 in alignment withthe respective light emitting elements 611 of the first region 606, asecond region average white point is provided by virtue of providing thesecond wavelength conversion layer 612 in alignment with the respectivelight emitting elements 610 of the second region 608, and wherein thefirst region average white point and the second region average whitepoint are substantially the same. The spectral characteristics of thefirst wavelength conversion layer 618 may be different to the spectralcharacteristics of the second wavelength conversion layer 612, that isthe spectrum that is output for a given light emitting element input isvaried.

Alternatively or in combination, the white point can be adjusted byleaving some of the light emitting elements uncoated. Thus the number oflight emitting elements 610, 611 that have a wavelength conversion layercan be used to adjust the white point of the respective regions 606,608. Thus a method of manufacturing an illumination apparatus maycomprise the steps of forming a non-monolithic array of light-emittingelements 611 on a support substrate 500; for at least some of thelight-emitting elements 611 in a first region 606 of the supportsubstrate 500, measuring their combined spectral output; providing afirst wavelength conversion layer 618 in alignment with some of therespective light emitting elements 611 of the first region 606, whereinthe number of light emitting elements 611 of the first region 606 thatare provided with the first wavelength conversion layer 618 is adjusteddependent upon the measured combined spectral output from the measuredlight emitting elements 611 of the first region 606; for at least someof the light-emitting elements 610 in a second region 608 of the supportsubstrate 500, measuring their combined spectral output; and providing asecond wavelength conversion layer 612 in alignment with some of therespective light emitting elements 610 of the second region 608, whereinthe number of light emitting elements 610 of the second region 608 thatare provided with the second wavelength conversion layer 612 is adjusteddependent upon the measured combined spectral output from the measuredlight emitting elements 610 of the second region 608. The first andsecond wavelength conversion layers 612, 618 may be the same.

Alternatively or in combination, the white point can be adjusted byadjusting the thickness of the wavelength conversion layer. Thethickness may be adjusted by varying the solvent fraction of the layers612 and 618, or by adjusting the thickness of the stencil 620 to bedifferent for different regions 606, 608. The thickness refers to thethickness of the layers 612, 618 after processing (for example afterbaking to remove solvent). Thus a method of manufacturing anillumination apparatus may comprise the steps of forming anon-monolithic array of light-emitting elements 611 on a supportsubstrate 500; for at least some of the light-emitting elements 611 in afirst region 606 of the support substrate 500, measuring their combinedspectral output; providing a first wavelength conversion layer 618 inalignment with the respective light emitting elements 611 of the firstregion 606, the thickness the first wavelength conversion layer 618being selected dependent upon the measured combined spectral output fromthe measured light emitting elements 611 of the first region 606; for atleast some of the light-emitting elements 612 in a second region 608 ofthe support substrate 500, measuring their combined spectral output; andproviding a second wavelength conversion layer 612 in alignment with therespective light emitting elements 610 of the second region 608, thethickness of the second wavelength conversion layer 612 being selecteddependent upon the measured combined spectral output from the measuredlight emitting elements 610 of the second region 608.

FIG. 45 shows that the light emitting elements may be provided instrings wherein the string electrodes 624, 626 connected to lightemitting elements 610 in region 608 cover a number of bin regions withinthe region. Thus the deviation about the mean of the total forwardvoltage across the string is reduced, advantageously simplifying sometypes of driver design and reducing cost.

FIGS. 46a-f shows a method to form an array of light emitting elementsfor embodiments wherein the semiconductor epitaxial growth substrate 630is not adequately transparent (in an electromagnetic wavelength band) toa suitable or desirable illumination wavelength for a lift off processsuch as a laser lift off process. Alternatively, the lift-offinteraction layer may not be well suited to a desirable laser. Forexample, as shown in FIG. 46a , the semiconductor growth substrate 630may be silicon or silicon carbide on which a light emitting elementlayer 632 is grown for example by known epitaxial growth methods. Suchmaterials are typically substantially absorbing to the ultravioletradiation wavelength band typically used in excimer laser lift off atGaN-sapphire interfaces. Alternatively the laser lift off process maynot be sensitive to electromagnetic radiation of a desirable lightsource. For example the interface of GaN-sapphire is not sensitive todecomposition in infra-red electromagnetic radiation in comparison withthat is achieved by excimer laser illumination. Infra-redelectromagnetic radiation is a preferable electromagnetic radiationsource due to its lower cost compared to excimer laser sources.

A metallisation layer 631 may be applied to the top surface of the layer632 to provide electrical connection to the light emitting elementsfollowing an extraction step. The metallisation layer 631 may becontinuous or may be patterned. Further the metallisation may besuitable for bonding to electrodes, for example by eutectic soldering toother layers on a substrate such as a support substrate which may be amothersheet.

FIG. 46b shows that a support substrate 520 that is transparent in anelectromagnetic radiation wavelength band may be attached to the layer632 by means of an absorbing layer 634 that is absorbing in theelectromagnetic wavelength band. The layer 634 may comprise for examplean ultra-violet sensitive tape (wherein adhesion strength is lowered bymeans of an illuminating UV laser) or may an infra-red absorber (whereinadhesion strength is lowered by means of infra-red radiation). In eachcase, an array of patterned electromagnetic radiation beams 529, 530,531 is used to illuminate the layer 634 in alignment with light emittingelements 532 that are desirably removed.

In a further step, layer 632 is removed from substrate 630 for exampleby means of an etch step, a photochemical etch or known lift offtechniques to provide a structure of substrate and layers as shown inFIG. 46c . Further metallisation layers 633 may be applied to theopposite side of the light emitting element layer 632 compared to themetallisation layer 631.

Further layers (not shown) such as silicon dioxide may be arrangedbetween the layer 632 and substrate 630 to facilitate or improve thereliability of the separation, for example by means of wet etching orphotochemical etching. The separated structure of FIG. 46c may then bepatterned to provide an array of light emitting elements with separations1, as shown in FIG. 46d , for example by means of laser scribing oretching.

As shown in FIG. 46e in a similar manner to that used for FIG. 36a , apatterned array of optical illumination regions 528 in theelectromagnetic radiation wavelength band is provided so as to provide apatterned lift off of light emitting elements with separation s1 ontosupport substrate 636 as shown in FIG. 46f . Residual material of layer631 on elements 532 may be cleaned after the extraction step.

The substrate 636 may then be aligned with an array of optical elements,or may comprise the optical elements, for example as shown by opticalelement array structure 41 of FIG. 9; or may comprise an intermediatetransfer substrate that is used to transfer the elements 532 onto asubstrate 67 or optical element array structure 41.

Thus a method of manufacturing an illumination apparatus may comprisethe steps of forming a monolithic light-emitting layer 632 on anelectromagnetic radiation wavelength band absorbing substrate 630;transferring the monolithic light-emitting layer 632 to aelectromagnetic radiation wavelength band transmitting substrate 520;selectively removing a plurality of light-emitting elements 522 from themonolithic light-emitting layer 632 in a manner that preserves therelative spatial position of the selectively removed light-emittingelements 522 by selectively illuminating the monolithic array oflight-emitting elements 522 through the electromagnetic radiationwavelength band transmitting substrate 520 with electromagneticradiation in the electromagnetic radiation wavelength band; forming anon-monolithic array of light-emitting elements 532 with the selectivelyremoved light-emitting elements in a manner that preserves the relativespatial position of the selectively removed light-emitting elements; andaligning the non-monolithic array of light-emitting elements with anarray of optical elements.

Thus method of manufacturing an illumination apparatus comprises forminga monolithic light-emitting layer 632 on a first substrate 630;transferring the monolithic light-emitting layer 632 to anelectromagnetic wavelength band transmitting substrate 520; selectivelyremoving a plurality of light-emitting elements 532 from the monolithiclight-emitting layer 632 in a manner that preserves the relative spatialposition of the selectively removed light-emitting elements 532,performing of the selectively removing comprising selectivelyilluminating the monolithic array of light-emitting elements through theelectromagnetic wavelength band transmitting substrate 520 with light inthe electromagnetic wavelength band; forming a non-monolithic array oflight-emitting elements with the selectively removed light-emittingelements 532 in a manner that preserves the relative spatial position ofthe selectively removed light-emitting elements 532; and aligning thenon-monolithic array of light-emitting elements 532 with an array ofoptical elements. The first substrate 630 may be an electromagneticwavelength band absorbing substrate.

Advantageously, the absorption of the material or materials forming thelayer 634 may be optimised for use with the wavelength band of theelectromagnetic radiation source such as a laser used to provideillumination regions 528. For example, the laser may be an excimer laserwith an ultraviolet wavelength band emission, for transmission through asubstrate 520 comprising quartz or sapphire material. The material ofthe layer 634 may however have a wider process window than the galliumnitride to sapphire adhesion process window that may increasereliability and reduce process time. Alternatively an infra-red laserwith an infra-red electromagnetic wavelength emission band may be usedin combination with a substrate 520 comprising a glass or plasticsubstrate. Advantageously, infra-red electromagnetic radiation sourcessuch as diode pumped solid state lasers may be provided with high powerand low cost compared to excimer lasers. Thus, the throughput yield ofthe patterned laser lift off may be improved and the cost reduced.Further the beam uniformity requirements for illumination of layer 634may be less tight than for UV excimer laser lift off, providing Gaussianbeam exposure conditions and reduced probability of cracking of thelayer 632 during the extraction step of FIG. 46e . Further, thesubstrate 630 may advantageously have reduced cost (for example silicon)compared to the sapphire epitaxial growth substrate of FIG. 36a reducinglight emitting element cost. Further, the lattice constant of theepitaxial growth substrate 630 may be more closely matched to thelattice substrate of the semiconductor material of layer 632 (forexample silicon carbide); thus reducing strain in the device andimproving light emitting element performance.

While at least one exemplary embodiment has been presented in theforegoing detailed description, it should be appreciated that a vastnumber of variations exist. It should also be appreciated that theexemplary embodiment or exemplary embodiments are only examples, and arenot intended to limit the scope, applicability, or configuration of thepresent disclosure in any way. Rather, the foregoing detaileddescription will provide those skilled in the art with a convenient roadmap for implementing an exemplary embodiment, it being understood thatvarious changes may be made in the function and arrangement of elementsdescribed in an exemplary embodiment without departing from the scope ofthe present disclosure as set forth in the appended claims and theirlegal equivalents.

The invention claimed is:
 1. A method for manufacturing an illuminationapparatus, the method comprising: forming a monolithic array oflight-emitting elements; selectively removing a plurality oflight-emitting elements from the monolithic array by adhering them to afirst adhesive substrate in a manner that preserves the relative spatialposition of the selectively removed light-emitting elements;transferring the plurality of light-emitting elements from the firstadhesive substrate to a second adhesive substrate in a manner thatpreserves the relative spatial position of the selectively removedlight-emitting elements; and transferring the plurality oflight-emitting elements from the second adhesive substrate to a supportsubstrate in a manner that preserves the relative spatial position ofthe selectively removed light-emitting elements; wherein the pluralityof light-emitting elements that are selectively removed from themonolithic array are selected such that, in at least one direction, forat least one pair of the selectively removed light-emitting elements inthe at least one direction, for each respective pair there is at leastone respective light-emitting element that is not selected that waspositioned in the monolithic array between the pair of selectivelyremoved light-emitting elements in the at least one direction.
 2. Themethod according to claim 1, wherein each of the plurality oflight-emitting elements comprises a p-doped layer comprising a p-dopedsurface.
 3. The method according to claim 2, wherein the plurality oflight-emitting elements are adhered to the first adhesive substrate suchthat their p-doped surfaces are in contact with the first adhesivesubstrate.
 4. The method according to claim 2, wherein the plurality oflight-emitting elements are transferred to the second adhesive substratesuch that their p-doped surfaces are exposed.
 5. The method of claim 2,wherein the plurality of light-emitting elements are transferred to thesupport substrate such that their p-doped surfaces are in contact withthe support substrate.
 6. The method according to claim 1, wherein theadhesive force of the light-emitting elements to the second adhesivesubstrate is greater than the adhesive force of the light-emittingelements to the first adhesive substrate.
 7. The method according toclaim 1, wherein the adhesive force of the light-emitting elements tothe support substrate is greater than the adhesive force of thelight-emitting elements to the second adhesive substrate.
 8. The methodaccording to claim 1, wherein the support substrate comprises a planarsubstrate.
 9. The method according to claim 1, wherein selectivelyremoving the plurality of light-emitting elements comprises selectivelyilluminating a plurality of the light-emitting elements with anillumination that separates, at least to an extent, the selectedlight-emitting elements from a substrate.
 10. The method according toclaim 9, wherein the selective illumination comprises a plurality ofshaped laser beams.
 11. The method according to claim 9, wherein theselective illumination comprises electromagnetic radiation in theultraviolet wavelength band.
 12. The method according to claim 1,further comprising aligning the light-emitting elements with an opticalelement array structure comprising an array of optical elements.
 13. Themethod according to claim 1, wherein the light-emitting elements eachhave a maximum dimension of 0.1 mm or less.